DGS2 and I have just passed 40 happy minutes with me casting stitches onto a knitting needle and him slipping them off and unravelling them, then rolling the wool carefully back up, then again, and again. Fairly restful for me and a bit of counting thrown in. Unfortunately he's now moved on to painting very messily creatively... 
He's 3, and we look after him Mondays and Wednesdays. We set off to his house at 0630h and get home at 1900h, so Tuesdays have been our rest and recovery days. As of tomorrow we're looking after DGS3, 18 months, on Tuesdays at his house too, so will have to raise our game!
They're gorgeous boys and we're delighted to be able to help out and build up close relationships with them. The housework can go hang.