Any turkey shell will have stout recoil in that light gun. People seem to not make the connection between rifles and shotguns when it comes to recoil. We would never hand a child a rifle that kicks like a lightweight 20 gauge. The only way to get good turkey power performance with low recoil in a light 20ga is to roll your own shells with small tungsten shot.
If you don't want to handload, my advice is get a Sumtoy 562-5 and the heavyweight or TSS shells from Federal. Use it yourself. If you're used to a 12 gauge with lead shells you will be astonished. Also get a .410 and a SumToy choke and Federal TSS shells for the kids. Put a red dot on it to help place the tight pattern.
Otherwise, get some low recoil 3/4oz shells for practice with the 20 and only allow shooting of the turkey loads at the turkey. If the kid is trained to hold the gun correctly and is appropriately excited, recoil will go unnoticed. Training means holding it tight into the shoulder, off the collar bone and with the thumb held to the side to avoid a bloody nose.