Little helpers

My kids are almost six and almost three. They are such good helpers at this age and it makes you wonder why it is that things like clearing trees and feeding animals are chores to us but fun to them(okay so I don't really count feeding animals as a chore because I secretly enjoy it) When do these things stop being fun and start being work? My kids were fighting over a hand saw today(I know, kinda scary) because they both wanted to help their dad cut fence rails. There we were sweating and swearing and wanting a coffee break and they were fighting over who's turn it is to saw down trees. I guess I had better appreciate their helpfulness now because these things are likely short lived. There will come a day when offering to tickle them won't be payment enough anymore. *Sigh* They grow so fast!