Lots of places. St Louis RV Park is an option. Very bad part of town after dark. Park is very secure, but outside the park can be dangerous. Casino Queen. Jellystone Park in Eureka. KOA in Eureka, Pin Oak Creek RV Park in Villa Ridge. Babler SP in Wildwood (or maybe Manchester). Robertsville SP in Robertsville. 370 Lakeside RV Park in St Peters. Sundermeiers RV Park in St Charles. (Washington SP or St Francois SP-a little farther out, but nice parks). 370 Lakeside will give you deep discounts to the St Peters? REC-PLEX. A very unique rec building with numerous things to do (including but not limited to swimming).
If you are going to be in town a few days. With a 12 year old boy, I would highly recommend Jellystone or KOA. These parks are next door/across the road (respectively) from Six Flags St Louis (in Eureka). Jellystone offers deep discounted SFSL tickets and a pancake breakfast. Jellystone always has kid related activities and a pool. They can likely help you out with Cardinals tickets too.
SFSL has TWO (2) complete theme parks for one price. The rides park has 8 roller coasters (one is brand spankin new). The water park has numerous slides, tornado ride, lazy river, wave pool.
Tim-DW(Kathy)
12 Chevy Sonic DD, 03 JEEP GRAND CHEROKEE, 2001 Jayco KIWI
If a "nightmare" is considered a dream-then I am living the dream