Some online sources say don't put peppermint oil on a baby others say you can dilute and use on babies feet. Which is right?

Personally, I wouldn't put essential oils on baby directly. Essentials can be quite "strong" on baby's delicate skin. What do you need it for? if you are using peppermint oil to soothe congestion or for a cold, perhaps you can add a few drops of peppermint oil to a room diffuser or spritz diluted peppermint oil to the general area of baby's room.