Hi Bagel,
Is your concern that you son is too physically affectionate with a helper / employee? Or it is a hygiene thing?
Because I think complex instructions would only be confusing to a 2-year-old.
"You can kiss mommy and daddy, but not the woman who cares for you all day." For a young child displaying natural joy and affection, this would probably feel weird.
(Warding your kid off strangers is a totally different matter).
Or would you say, "you can kiss the helper, but without saliva." I don't think a 2-year-old really has that much control over his drool!
Sometimes, I think we adults project our own worries onto kids who are quite clueless. Does a clumsy toddler have tcontrol / thought over exactly where and how he's kissing someone?
My little girl is much younger -- 1 year-- but she's already super affectionate. (And super drooly!)
She hugs everything -- me, dad, her favorite toddler friend in the playgroup, her toys, her cousin, and my helper. And my helper will occasionally give her a peck back on the cheek of the top of the head.
I'm thrilled that they have such a good relationship.
My child's daily happiness with her carer is more important than any feelings of jealously I may have as a mom.
As for the hygiene thing -- well, my helper changes her diaper, bathes her, feeds her her food, wipes her snotty nose when she has a cold. I don't think a kiss is going to spread any more germs than will already be spread. (That said, they don't kiss on the lips)