I am possibly the worst harness punter ever but here are my early thoughts:
4yo boys: Lennytheshark (best bet of any age group)
4yo girls: No idea
4yo Trotters: Even less idea
3yo boys: Lettucerockthem (sorry harvs!)
3yo girls: Nike Franco (next best)
3yo Trotters: ???
2yo boys: Birdy Mach
2yo girls: Katy Perry (if she goes that way??)
2yo trotters: Elkjay Phoenix
I've probably stopped a few there too!!