Can a kid playing Rec U12 soccer legally be red carded? Supposedly not but I cannot find any rules about that. Any refs on here?

Any modifications to the laws of the game would be at the league level. There are no laws at IFAB/FIFA/USSF level which do not allow the ejection/red card of a U12 player. Unless it is a highly competitive level, it is typically accepted that cards aren't used at the lower ages. Asking a coach to remove and talk to a player is often the way it is done. Again, however, unless the league has a rule on this, there is nothing stopping a red from being shown.