WILDLIFE SHOWN IN EXHIBITS: Several varieties of wildlife are already on exhibit at the Children's Museum on Wall St., which is being operated by the Children's Museum Association. The children shown above are inspecting live specimens, including white mice, a gartersnake, a frog and small turtles. The museum is open now from 2 to 3 o'clock Monday and Wednesday afternoons. Association officials hope to expand greatly the collection available at the museum, the hours and the activities. The museum is being, and will be, supported by public contributing memberships.