Having tackle that fits and is easy to use is also important. Have your children hold the rod in their hands and check their grip. Little fingers that don't wrap around well will lose grip, and the rod will be lost in the water. Purchase a small tackle box for their tackle, snacks and toys. Explain about sharp hooks before you have to dig one out.
Small children have difficulty casting but love to retrieve, so offer to assist with the cast.
If they are missing bites, offer to help with setting the hook, then hand the rod back to the child. My husband, Sam, or I would set the hook, and Colby would be ecstatic as he pulled crappie or sunfish out of the water. He got the feel of a fish on the other end of his line and gained confidence that helped him begin setting the hook himself. Keep a watchful eye to see what the child can do. Offer to help but be understanding if they want to try to do everything themselves.