My daughter LOVES chalk but I have to watch because she will eat it. She just likes to be outside. She plays on her brothers 4 wheeler or climbs on the tricycle and pushes herself around with her feet. She likes to play in the kiddie pool too. We have a playhouse and little tikes slide too.
A kiddie pool or a sprinkler would be so fun. Another thing my dd liked to do was finger paint... I would spread out an old shower curtain and strip her down to a diaper and let her go at it. She LOVED it. Of course, look for the crayola finger paint, they are non toxic bc she will probably end up eating some...lol.
Also, I would like to add that crayola finger paint is washable and comes out of most any fabric in the wash, and all you have to do to get it off your kids is spray them down in the bathtub. no stains!