My suggestion to get all these activities is a 14-day itinerary in Tanzania + Zanzibar.

Dates: Any two weeks in the dry season (June–Oct best overall; Dec–Mar works too). Best months depend on whether you want migration camera action.
Pace: Active but family-friendly — 3–4 nights on safari, 1–2 nights in the Kilimanjaro foothills for rainforest/waterfall, then 6–7 nights on Zanzibar beaches with snorkeling day-trips.

Day 1 — Arrive Kilimanjaro or Arusha (Tanzania)

Fly into Kilimanjaro International Airport (JRO) (or Arusha via JRO). Transfer to Arusha (the safari hub) or a family hotel near the airport. Rest, short market walk, early bedtime.
Tip: pick a family-friendly hotel with a pool to recover from travel.

Day 2–5 — Northern Safari (Tarangire + Ngorongoro or Serengeti loop)

Two family-friendly options — (A) shorter / easier drives & elephants: Tarangire + Lake Manyara + Ngorongoro; (B) classic big-game + migration: Serengeti 3 nights. Both are excellent for kids.

Suggested plan (A — gentler for kids):

Day 2: Tarangire National Park — elephants and baobabs, game drive in morning + afternoon.
Day 3: Lake Manyara (tree-climbing lions, flamingos) then drive to Ngorongoro rim lodge.
Day 4: Full day in Ngorongoro Crater — the crater floor is compact and wildlife-dense (great for children to see many species in one day). (Tanzania Tourism Gateways)
Day 5: Transfer back to Arusha; evening flight or drive to Kilimanjaro / Moshi area (see Day 6).

If you prefer Serengeti (B), fly or drive to Serengeti for 3 nights — choose a family tented camp (kids-friendly activities, short drives).

Family tips:

Short morning and afternoon drives; mid-day rests at the lodge; choose camps with family rooms or connecting rooms.
Bring motion-sickness remedies for bumpy roads.

Day 6 — Transfer to Kilimanjaro foothills (Moshi area)

Drive ~2–3 hours from Arusha to Moshi / Materuni area (the classic base for rainforest/Chagga village visits). Check into a family-friendly guesthouse.
Relax, visit local market or hotel pool.

Day 7 — Materuni village, coffee tour & waterfall (rainforest day)

Materuni is a short, family-friendly rainforest hike with waterfalls, shady coffee farms and easy local culture experiences — a great rainforest introduction without steep treks. The walk is suitable for children and offers coffee tours, waterfall swims and village encounters. (materunicoffee.com)
Photography: misty forest, banana terraces, waterfall portraits — use a fast prime for low light under the canopy.
Return to Moshi for overnight. (If everyone is energetic, add a short evening cultural performance.)

Day 8 — Flight to Zanzibar (or return to Arusha then fly)

Transfer to Kilimanjaro Airport (JRO) and fly to Zanzibar (ZNZ) — direct flights are about ~1 hr 5 min. A short hop keeps kids happy and travel smooth. (Skyscanner)
Arrive Zanzibar, transfer to a beach resort (Nungwi, Kendwa, or east coast Jambiani/Jozani depending on vibe: Nungwi/Kendwa = lively beaches; east coast = calm lagoons).

Day 9–13 — Zanzibar: snorkelling, beach, cultural days

Day trip to Mnemba Atoll or nearby reefs for family-friendly snorkeling with coral gardens, tropical fish and shallow reefs perfect for kids — Mnemba, Nungwi and Kizimkazi are top options. For variety, book a snorkel trip to Nakupenda Island or a boat trip to Mnemba for snorkeling and picnic. (Snorkeling Report)
Jozani Forest visit (see red colobus monkeys) — an easy short guided walk that’s nice for families.
Spice Tour — short, fun, educational and kid-friendly.
Relaxing beach days, sunset dhow cruise (great family photo ops), and optional dolphin-watching at Kizimkazi.

Snorkelling tips for kids:

Use shallow, protected reefs where currents are low (Mnemba lagoon is ideal). Bring rash vests, reef-safe sunscreen, and child lifevests if nervous.

Day 14 — Fly home via Kilimanjaro / Dar es Salaam

Morning at the beach, transfer to Zanzibar airport for flight home (via Dar es Salaam or Kilimanjaro depending on routing).

Logistics & Practicalities

Internal flights & travel time

JRO ↔ ZNZ direct flights ~1h 5m (several daily options). Book domestic flights early. (Skyscanner)
Safari transfers typically by 4×4 or short scheduled flights if using Serengeti; choose based on family tolerance for driving.

Where to stay (family-friendly picks)

Safari: family tents or family suites in lodges around Ngorongoro, Tarangire or Serengeti (ask operator for connecting rooms, kids’ menus).
Kilimanjaro area: family guesthouses in Moshi with pools and easy Materuni access.
Zanzibar: family resorts in Nungwi/Kendwa or boutique beach houses in east coast villages. Book beach properties with safety and snorkel gear included.

Booking & operators

Use reputable local safari operators (licensed guides), and book internal flights + park permits through your tour operator or lodge.
Ask hotels for family transfers, child meals, and babysitting if needed.

Health & Safety (important for families)

Vaccinations & malaria: Check official travel-health guidance and get needed vaccines & malaria prophylaxis. The CDC has the latest Tanzania travel health recommendations — consult them and your travel clinic 6–8 weeks before travel. (CDC)
Water & food: Use bottled or filtered water; avoid raw salads unless at trusted properties.
Sun & reef safety: Reef-safe sunscreen, rash guards for kids, life vests for non-swimmers.
Travel insurance that covers medical evacuation and activity coverage (snorkeling, jeep safaris) is mandatory for peace of mind.

Family & Kid-Friendly Notes (for your 12-year-old)

Safari is very accessible and great for kids 6+. Walking safaris in Mole were mentioned earlier — in Tanzania stick with vehicle safaris (unless guided short walks at lodges).
Materuni waterfall hike is manageable for a 12-year-old and gives rainforest exposure without multi-hour climbs. (materunicoffee.com)
Gorilla trekking has age restrictions (usually minimum 15 years) — so gorillas are not family-friendly for a 12-year-old. If gorillas are a must for later trips, plan a separate Rwanda/Uganda trip when your son is older. (Happy to help plan that later.)

Best Time to Travel (quick guidance)

Overall best: June–October dry season — excellent wildlife viewing and good snorkeling conditions.
Migration timing: If you want to see the Great Migration river crossings, timing differs by month — tell me if you want migration and I’ll time the trip precisely. (Serengeti)

Budget Estimate (very rough, per family of 3–4)

Mid-range safari + flights + lodges + Zanzibar resort: expect $6,000–$12,000 USD per person for a comfortable family itinerary (depends heavily on lodges, internal flights, and season).
Lower budget: self-drive & budget lodges can reduce costs substantially; luxury lodges increase price.

Packing checklist — family edition

Lightweight layers, sun hat, sunglasses
Lightweight waterproof jacket (safari mornings can be chilly)
Good walking shoes + sandals for beach
Reef-safe sunscreen, rash guard for kids
Binoculars + camera + telephoto lens (70–200mm or 100–400mm recommended)
Plug adaptors, power bank, spare batteries
Child medications, rehydration sachets, insect repellent
Copies of passports, insurance, emergency contact list

Photography tips (family + travel photography)

Safari: telephoto 200–400mm, monopod optional, shoot RAW, short bursts for action.
Materuni rainforest: fast prime (50mm f/1.8 or 35mm f/1.8) for low light, capture village life and waterfall portraits. (Tripadvisor)
Zanzibar snorkeling: use waterproof housings or a compact underwater camera/snorkel mask camera; shoot at shallow reefs mid-morning for best light. (Snorkeling Report)

Alternatives & variations

If you want gorillas (instead of Materuni): plan a separate Uganda or Rwanda trip — gorilla permits and minimum age rules apply (usually 15+) so not suitable for a 12-year-old right now.
If you want more rainforest: replace Materuni with a short trip to Mahale (for chimpanzees) or Nyungwe (Rwanda) — but both add flights/complexity.
If you want quieter islands: consider Pemba (more pristine snorkeling) instead of Unguja (Zanzibar main island). Pemba is wilder and excellent for family snorkel trips. (africasafaristours.com)

Quick reference links (planning resources)

Official Tanzania tourism site. (tanzaniatourism.go.tz)
Materuni waterfall & village info (family rainforest day). (materunicoffee.com)
Kilimanjaro (JRO) → Zanzibar (ZNZ) flight info (short hop ~1h5m). (Skyscanner)
Best snorkeling sites in Zanzibar (Mnemba, Nungwi, Kizimkazi, Nakupenda). (Snorkeling Report)
CDC travel health & malaria guidance for Tanzania — check before you go. (CDC)

FAQs (short)

Q: Is this itinerary safe with a 12-year-old?
A: Yes — the plan avoids strenuous treks and includes family-friendly activities. Always book family rooms and ask lodges about child policies.

Q: Can we swim with dolphins?
A: Dolphin-watching tours operate (Kizimkazi), but ethical swimmer interactions vary — I recommend observation and responsible operators.

Q: How fit do we need to be for Materuni?
A: Moderate fitness; the walk to the waterfall is 30–60 minutes depending on route, family-friendly.

Q: Do I need travel insurance?
A: Yes — include activity coverage and medical evacuation.

Q: How much advance booking?
A: Book internal flights and safari lodges 3–6 months ahead; high season up to 9–12 months for top camps.

Best Family Trip to Africa — Safari, Rainforest & Snorkeling