As soon as possible. Make sure they have elbow and kneepads as well as ttheir helmets. They'll fall a lot and that protection helps. I'm always impressed with the inate tenacity these of these little guys. Fall, get up, fall, get up..over and over. Take periodic videos using the same disc (or whatever media you use). You'll be surprised with the progress, and the kids will enjoy watching them later. I take videos during the year of my grandchildren. Part of every Christmas is spent with them huddled around a TV, seeing themselves in their games. When my youngest grandson had just turned 4, I took him to an early season practice. At one end of the ice was a four to six year-old learning session. At the other end were 6-8 year olds getting picked for teams. He had the attention span of the usual kid of 4, so he kinda drifted from one instructor to another in the learning group. I'm sitting on the bench, and he comes over to me to ask if I'd buy him a slushie after his session. I tell him yes, and he skates away. But, he doesn't go back to the little kids. He goes to the end where they're choosing teams. After a litttle while, I see one of the coaches with a clipboard, copying his name and telephone number from the tape on his helmet. I'm a grampa, so I shut my mouth. But, that's how come he made one of the teams a couple years early.