dd is now 12. We took her to Panama and Costa Rica last summer which she loved - beaches for snorkelling and scuba, turtle watching, zip wire, guided walks in rainforests, white water rafting.
The year before we went to Burma and Thailand. She wasn't that interested in Burma (too many temples!) but loved Thailand.
We went to Sri Lanka when she was about 7 or 8. That also went down well - beaches, elephant orphanage, jungle.
When she was 5 we went to Singapore, Malaysia and Borneo - we had 4 weeks, so it would be too much to cram into a shorter holiday. She particularly liked Kuala Lumpur (Petroasains Science Discovery Centre, skywalk in PETRONAS Towers, water park and canopy walkway) and Borneo (orang utan rehabilitation centre and a few days in a jungle camp).
We've also been to India a couple of times, but I'd avoid that for a first long haul for children as it could be too much of a culture shock. We also took dd on trips to South Africa and Australia when she was a toddler. They could be good for a first long haul trip, because of language, food and health (although I do remember that we had to avoid Kruger Park as that part of SA was malarial and dd was too young for malaria tablets).
Just remembered. We also took dd to Indonesia - Bali, Lombok and Rinca. That was another one that she enjoyed.
I'd definitely avoid Sharm. Haven't been there, but a friend who worked there as a dive instructor said it's pretty soulless. There's loads of better options that adults and children can all enjoy.