A visit to Thailand will certainly broaden the horizons of young visitors, and many families report great experiences in the kingdom, partly because most Thais dote on kids. Larger resorts and hotels have kid-friendly programs, kids' clubs, connecting rooms, sports equipment rentals, and kid-oriented group activities. Many of the larger hotels also offer special deals for families or young children.
Some hotels allow kids under 12 to share their parents' room for free, especially if it has two double beds, but an extra bed can always be found at a small extra cost. There's not much point in looking for accommodation that includes kitchen facilities, as restaurants are generally inexpensive, but while the spiciness of Thai food appeals to most adults, you'll have to watch out for junior digging into a Thai salad laced with fiery chilies.
As in other countries, babysitting services are available in top hotels, but few consider this a chore in Thailand, and generally you can expect hotel and restaurant staff to be falling over each other to amuse the kids while you are eating or enjoying a snooze by the pool.
As to where to go for a family holiday, kids are as enthralled by tropical beaches and mountain landscapes as adults. Wildlife watching somewhere like Khao Yai National Park is a good idea, but you may want to give the ancient cities of Ayutthaya and Sukhothai a miss, as kids are likely to find the ruins a big bore.