BOSTON — April school vacation has arrived and state parks around Massachusetts are gearing up to help parents keep their kids busy in the coming week.The Department of Conservation and Recreation is offering a variety of what it calls family friendly programs in the state park system, including nature hikes, wildlife observation and mansion tours.DCR says most of the activities are free and many of the programs will be guided by agency staff.The list of parks offering April vacation activities covers nearly every region of the state.