My DS is 5 just after his February birthday I booked him I to swimming lessons, he goes once per week for a 30minute lesson. Around the same time his school started offering mini soccer straight after school so he does that too. But I wouldn't sign him up for anything else at the moment as he would be too tired. Also have DD who does brownies once a week and dance at after school club. I'm a sahm and I think 2 activities per week per child is the max I would allow them to do partly for financial reasons but partly because they would be too tired.