I can see Waithvine spending the night with the family even going so far as to using magic to make a birthday cake for the child. And then in the morning, telling the mom to "look in the cupboards" when he departs, and her seeing several lengths of braided elven hair with a note "Sell it carefully, and your farm will remain fed for some time". Or some useful advice like that. In addition to doing something like leaving the child a dolly or something to cuddle that looks like an elf, too. Because Wraithvine is just a kind soul like that, and he absolutely loves kids.