We just came back to the province from a 3 day trip to BKK. We went with 2 kids, 3 and 10 years old. If you need a hotel at a good location, i could recommend IBIS Riverside. If you book the Family room (around 1700฿/night), you will have a bunk bed for the kids and a Playstation 4 in the room????. Nice garden restaurant at the riverfront, good view, long and clean swimming pool and good access to the riverboats and BTS. Don't book the breakfast, there are many good and cheap options outside the hotel. And there is a 7/11 too.
We made a Tuktuk ride , it was a Hello Kitty Tuktuk????. Ask the guy from the restaurant near the street or the motorbike taxi guys. Ask for the price before you start the trip. We went to a nearby market (2x60 ฿) and next day to Lumpini Park (one way approx. 250-300฿). Lumpini park is just 15min. away, there you can rent a bicycle outside and drive around at the park.
And last but not least, i can recommend plane spotting at Suvarnabhumi airport (see map). Be sure to follow the red arrows because there is no U-turn if you come from PTT station. You can eadily park on the side line, great view of the planes, you get one every 2-4 minutes, Check flightradar app for arriving/departing flights.