There are probably hidden gems all over the country that I know nothing about, but I do know about an absolute prize just north of Chicago, in Skokie, called the Emily Oaks Nature Center.
The reason I love this place is that it PERFECT for very young children. It is small and compact. There is a hiking loop around a smallish pond that even toddlers can manage. They have outdoor picnic tables for snacks and an indoor interactive nature exhibit. On top of all that, there is a perfect little playground on the property. I have never been there when it was crowded or even really busy. Unless you plan on renting a room in the building, it is also free. It is a virtually ideal place to take a group of preschoolers. Here is a list of all available educational programs.
When my boys turned 3 and 1, we hosted a joint birthday party at Emily Oaks Nature Center. I found these bug collection boxes at the Dollar Store ( I think they were 2 for a dollar in those days).
I took the tags off and painted the children’s names on the front. I then found a bag of cool bugs (used some old Halloween spiders) and each child received a bug box as their goody-bag. Total cost=just under $1.00 a piece. I’m nothing if not frugal.