There is also a botanical garden, I think it is called the Butterfly house. I haven't been there either.
They are 2 different things. The butterfly house is small (free I think) and in Forrest Park. The botanical gardens is a very large "garden" that costs to visit.
Actually, there are TWO different butterfly houses in St. Louis. There is a relatively small one inside the Zoo (in
Forest Park), which used to have an extra admission fee but is now free; it is part of the Monsanto Insectarium.
The larger and better (IMO) is the Sophia M. Sachs Butterfly House at
Faust Park in West St. Louis County. It is very large and has a butterfly themed accessible playground outside. Management of the facility was recently taken over by the Missouri Botanical Garden. The admission is $6 for adults and $4 for kids.
http://www.butterflyhouse.org/default.aspx
Faust Park is also the home of a wonderful antique Carousel in an indoor carousel house; those rides are $1.
The Missouri Botanical Garden (in South City just East of Kingshighway and south of I-44) is one of the top five botanical gardens in the U.S., and usually ranked as one of the top 10 in the world. If you like plants and gardening, this is a must-do stop. Lots of people don't think kids will like the place, but they love it -- trust me, I know -- I worked there for several years and I could see them enjoying themselves all day every day through the one-way glass mirrored walls of my office. The admission is $8 for adults, children are free.
http://www.mobot.org/visit/default.asp (Some of the fountains -- not all! -- allow splashing, so come prepared for that.)
Also, just FYI, with the recent reopening of the Magic House after their expansion, the price has gone up a bit. Admission is now $8 per person over age 1.
There are coupons for almost all the paid St. Louis attractions in our Entertainment Book, so you may be able to access those online if you have one for your area. Also, there is a St. Louis Family Attractions Card that also offers discounts at various places.
http://www.familyattractionscard.com/
PS: Note that Forest Park and Faust Park are two entirely different places. Forest Park is in the central city about 6 miles west of Downtown, but Faust Park is pretty far out in West County, in Chesterfield, over 20 miles west of Downtown. Forest Park was designed by Frederic Law Olmstead, the architect of Central Park in NYC, and is in fact larger than Central Park, by over 50%.