meadow if possible you could do a keep fit session. Either do running, jumping, stretching yourself, with some youths to help (also youths at the back to keep the kids in check), or put a you tube video on. We used a guy that did sessions for school (year 5) and it worked a treat.
Also with any year, including yr 5 and 6 (have a small prize) do sleeping lions, get youths to be watchers. Works well. But put those that are out in a 'pen' so that the alternative isn't more fun!
Do party games, statutes, pin the tail, flour game with sweet, chocolate with gloves etc.
Card pyramid, board games, winking murder game, print a load of colouring in sheets - much easier than crafts, do weaving with strips of card, origami - practise was ones first - the cat/dog, pac man origarmi are good. Get chop sticks and pasta to pick up and run with.
Google alternative sports day.
Anyway...sorry for the long post.