K.F.
T., I've been looking for indoor resources, too, since my daughter's birthday is at the end of January. She'll be three this year, and for the 2nd year in a row, we're doing Chuck E Cheese because she loves it and it suits her age. She's been to two birthday parties for 3-yr-olds at Bounce U (in Chesterfield, I don't know if there are any in St. Charles), and I found it a bit old for her. I wanted to do the Science Center (they have theme parties for different age groups), but they start at age three, so it probably wouldn't work for you. I'd check if there are any children's museums near you, they usually have parties for kids. My daughter has also been to parties at McDonald's with a play area. It's a cheaper option, and the kids always have fun there, too. Good luck making a decision!!
K.