My favourite theme for march break was always space. It appealed to the little kids with the stars and the big kids got into the aliens aspect of it. They can make rockets from boxes and space stations - which was only a dream of scientists back when my kids were on March break - or satelittes from assorted junk - can keep older kids happy for a few naptimes then hang in space from the ceiling.

March is a month of weired weather so our theme usually was weather since over the month you get everything from rain, hail, sleet, snow, wind, fog, etc. Rainbows are part of weather which leads into the leprechauns and their secret world at the end of the rainbow and then the sky where weather comes from leads into March break and a space theme.