Oh boy, oh boy, so many experts, that all went to Pattaya and still failed to look further then the bars and the gogo girls.

Actually Pattaya is not a typical destination for families, but there's a lot to do with smaller children:

Mini Siam
Pattaya Water Park
Sri Racha Tiger Zoo
Million Years Stone Park
Pattaya Underwater World
Ripley's believe it or not
Noong Nuch Garden

just to mention a few. It still stinks compared to places like Disney Land, Universal Studios or Sea World, but my son (at that time 2 years old) old and the two 5 year old nices of my wife had a lot of fun in Pattaya. If you choose your hotel wisely (out of central Pattaya area), there are worse places in Thailand to stay with kids

In Bangkok I can recommend places like Dream World, Safari World, Dusit Zoo, Siam Ocean World, the Water Park at Central Bangna or Funarium.

If you want to go to the south then Phuket might be to consider. Centara Grand West Sands Resort & Villas Phuket and both Centara Resorts at Karon offer great facilities for children (there are definately much more kid friendly hotels in Phuket). And there's a lot ot do for kids in Phuket as well: elephant rides, a butterfly farm, a gibbon rehabilitation project, a huge water park at Haad Mai Khao, the aquarium ar Cape Panwa and more.