Here's an easy and cheap art project that would be a great end-of-the-year activity. It can be finished in a few hours all in the same day.
Use leftover construction paper, magazines, and even notebook paper. Keep the engaged while you tidy up for the summer.
Take some left over paint, any color, and paint over a magazine pager or on newspaper. Draw fish on old paper, too. We used notebook paper for these fish. Trace them with any color marker and color them. Draw some patterns on top. Look at the red fish with purple fins. This fish was colored lightly and then the patterns were drawn on top with the same exact crayon. Draw some circles on any color construction paper to look like bubbles. Cut some sea plant shapes out of the magazine papers once the paint dries. If you use a thin layer of paint, it will dry in an hour or so. Cut it all out, layer/arrange, and glue.