My DD weaned just after her 5th birthday, and likes to rub my belly for comfort. So we'll cuddle up and she'll do that. I set boundaries--no poking me in the belly button, and no rubbing my breasts. We've talked about privacy and personal boundaries, regarding that, as well as regarding appropriate ways of climbing into her dad's lap...and how this applies to her, as well as to grownups.
Anyway, she used to bug the heck out of me by rubbing my belly while nursing, but I find I don't mind it so much, usually, now that she isn't nursing. I do seem to be the only lovey she's ever had, no fave blanket or stuffed animal or fingers to suck on here, so I'm in no rush to make her outgrow it.