Kids don't always have the patience to learn to catch fish with fake bait. So using live bait on a kid's rig allows them to deadstick and significantly increases their chances of catching fish, big and small.
Junior often gets distracted. Use a rod holder stake, otherwise when he decides to put the rod down to chase bugs it could get pulled in the lake. I've seen it happen.
You can buy a kids combo spincasting rod for under $30. Use a Gamakatsu size 2 hook with half of a live nightcrawler on it. Cast it out there, let it sit, and watch the bobber. When the bobber goes under reel in.