M.A.
"Kid City" near Lowry Park zoo used to have one day a month that was free, but I dont remember what day. You can find them in the phone book or yellow pages online.
I got a 4-person membership to aquarium for $110 and get free or discounted admission to lots of places in Tampa area.
Many libraries have an art/craft day & similar at least monthly.... check local rec centers too.
Welcome to FL!!