Crafts are always fun. You could make sock animals, all you need are some hot glue guns, knee socks, stuffing and googly eyes. Yarn and felt are good too for decoration purposes.
Decorate your own little planter, and buy potting soil and plants to go in the planter afterwards.
If your neighborhood is amenable, you could send them on a scavenger hunt.
I don't think you'll need too many activities. Girls this age are pretty good about keeping themselves entertained.
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