Personally I would advise anyone against holidaying in Pattaya. Having been there once (as a male), the women pester you like flies. Although you can avoid this by staying within your hotel complex; much better to get out and explore the neighbourhood.
My first visit to Thailand was to Hua Hin and enjoyed it, good hotel, good uncrowded (very long) sandy beach, lively night market and lots of cheap eating out.
But if you are taking kids to Thailand, I would make sure that the hotel has lots of child friendly activities and take along all their electronic games.
If at 12 years of age, my parents had taken me to Thailand, the whole experience of such an exotic location would have kept me captivated throughout the holiday. Kids these days would be jaded without suitable entertainment during their stay. Check the cable TV offering of your chosen hotel as a potential source of entertainment on rainy days.
Don’t forget, our summer is their rainy season – when you get there, you will find out why they call it the rainy season.