Anything fun for kids in Longmont, Colorado besides the library and the museum?!?

I am a Nanny in Boulder and have a Nanny friend in Longmont who is not allowed to leave Longmont. We have been looking for fun activities to do with our charges, ages 2, 2, 4, and 6 months. We have been to the Library for story time and to the Museum, and we are looking for other fun things to do. We are both not familiar with the area, so were hoping to get some help! Oh, and I did an internet search and all I could find were cles and Bounce Town (which is too expensive to do all the time). Thanks!