I don't have children but I was sent an e-mail relating to this topic...The full story can be seen here - http://www.mrsciguy.com/teachstories.html#friend
I know I was part of many activities when I was a kid (scouts, camp, school band, etc.) and it was learning new things and trying many different activities that kept me motivated and engaged. I have a lot of self esteem because of things that I accomplished when I was a child (completed a 50 mille scout hike when I was only 11). I suggest giving praise when deserved, explaining what should have been done if they are wrong, and keeping them interested in extra activities.