The SLSC is a truly great place, no matter how old you are. We took our boys, ages 5 and 6, on Saturday through a company-sponsored event. We've been many times before as it's a great place to take kids on rainy or cold days, especially since it's free!
Since we were there on a special event, we had the opportunity to take in some "extras" we wouldn't normally do. We visited the Exploradome and the Monsters exhibit. I was a little worried about it being scary, but it wasn't at all. It might have been scary if the boys had ever seen any of the movies that the props were from, but they haven't so to them they were all just animals and creatures, not really monsters. While it was interesting, I didn't feel there was enough in there to justify the cost, so it was nice that we were able to visit for free.
We also got to see a planetarium show (Mr. Hubble's Universe), which was great! They pointed out different star formations and talked about how stars are made and the different types of clusters. Very informative and entertaining. This I would definitely pay for if we were to go again. The planetarium also hosts free star parties on the second Friday of each month from January to October. Weather permitting, there are a number of telescopes set up and staff on hand to help you view and answer questions.
There are also many free interactive presentations throughout the day at the SLSC. Many of them are held downstairs on the Centerstage. There are presentations on optical illusions, plastic, DNA, electricity, and temperature, as well as messy presentations like "Science Goes Splat"!
Tip: Parking next to the Science Center entrance costs $8. Ouch! But you can park on the street, or even better, go through Forest Park and park in the parking lots or on the streets next to the Planetarium. Parking there is free, and you can enter the planetarium and walk across the bridge over the highway to get to the Science Center. Then you also have the opportunity to check cars speeding down 64/40 with radar guns mounted on the bridge!