Greetings Ragtown, and welcome aboard.
You may need to start reloading or get in touch with a custom reloader. If your 6-year old can't handle the recoil of standard .410-bore target loads, then you might look into rim-fire, or pistol caliber "snake" loads. Or, as Buzzcook mentioned, reduce recoil by other means (my heavy comp O/U with a JS recoil reducer makes .410s kick like an air rifle).