My kids both do Aikido at the same club as me. The eldest is 10 and my youngest is 5.
They both love it, as much for the fun and exercise, as for any of the techniques. It's also nice for them to pick up the philosophy of Aikido. For instance, a while ago my eldest was trying to tickle me and the youngest yelled out "No! We learn Aikido so we can learn not
It was so cool!