Ideas for groups:

Books on the Square has story time for each age group and a multi-age group event on weekends.

parachute in the park (with a big sheet due to lack of parachute)
-stroller walks
-what is that smell? exploring new smells with the little ones
l-earning about baby sign language (maybe from an expert, depends on if I could find one to volunteer)
-story time at the library for babies
-baby book swap
-baby shower for a cause- bring in unused baby items that you received and don't have a use for to donate, do baby shower games at the same time and an excuse for cake
-opposites day- would work better with toddlers and older kids, meet some where and try to do as many things opposite than they are supposed to be. Works best if the parent/child work it into a full day of opposites (breakfast for dinner, etc.)