I wonder if you could read The Rainbow fish togehther and use it to talk about friendship and self esteem. Perhaps write or draw on the scales things that make us beautiful because we can share them (a smile, a hug, being helfpul etc) This would work really well as a celebration activity with a big fish (perhaps reflecting on what we want Messy Church to be like).
My husband and I, along with our 11 year old son, love to play foosball. We will play until our hands hurt. My little girls want to play so bad, so we let them drop the ball on the table. That only satisfies them for a little while.