I've looked through some state laws.

Some give a list of exceptions like "except for hygiene or medical needs."

Others say "it must be for sexual pleasure."

The latter puts pedos at risk: If you have to change a baby's diaper but you volunteer to do it because you know it will give you sexual pleasure, they can nail you if they can prove your motive.

On the flip side, if they can't prove your motive they you can touch a child's privates without needing to check the real reason against a prescribed list.

In some cultures, it's normal and expected that mothers will suck their infant son's penises to calm them down, not to get the mother or the son aroused. In states with the "for sexual pleasure" laws, in theory these mothers are not violating any laws. In practice child-services will probably take all the children away pending a full investigation and public humiliation. The kids will be reunited with the family only after the mother agrees that she made a mistake and agrees to ongoing monitoring.