This excursion has in favour that all visits are practically outdoors, which is appreciated by the kids. You can do it on your own by train + tuk-tuk (once in the city). It is not too far, about an hour from Bangkok.
You can add the temple of the monkeys in Lopburi.
A private group with or without a local guide are also good choices, in order to squeeze the available time. Especially if you include Lopburi in the itinerary because transfers might be exhausting and leave little time for visits if you do it on your own.
Take into account that trying to visit too many temples could be exhausting.
We suggest including the Bang Pa-In Summer Palace because its beautiful gardens are refreshing and the little ones will want to climb to the top of the observatory tower.
Think of the possibility of making the return trip on a cruise on the Chao Phraya River, highly recommended.