SInce the big kids will only be in care for a short time I would get a cardtable and 4 chairs set and just put it up and down as needed. You can make great use of the table with your toddlers by putting a blanket over it to make a playhouse - there are lots of patterns out there for sewing actual covers with themes like firestation/spaceship too but certainly not necessary when an old blanket or sheet serves the same purpose.

Just having a couple puzzles, maybe a game or two, some craft supplies like markers and construction paper, a couple pairs of scissors and glue sticks should be enough on hand for school age.

Besides I am assuming your plan is to get as many toddlers/preschoolers as you can since the before/after kids take up a space without producing any income in the sense they can pretty much eat for snack and use in supplies what you are paid for their care.