for begginers; simon says is one of the activities that is fun and easy.
for second grade a sing a song the name is "if you are happpy" this song has a good rhytm and says the movements that you have to do, so you are singing and at the same time you are doing the movements.
when i notice taht my students are boring or lazy I say some movements like .. shake your head , hand up, hands down, stomp youe feet, jump in one foot... thats fun for them.