another way to insure proper socialization is to reeeeally screen the takers.. and about immune system... well... I NEVER ever take a pup to a park until after all shot have been applied... but you can´t control that with strangers... I don´t remember how far your mom lives.. but is it a possibility to you offer and help to clean...

or... convince Dave... and when kids drop by just put the pups in a separate room/bathroom.. so they don´t have contact with each other...