That's pretty much an unsolvable problem.

If you tell someone their baby is ugly, not only do they don't believe it but they also hate you. You could anonymize it, but you're just back to even because they still won't believe you.

And to be fair, what would they do about it anyway? Trade it in?

All babies are ugly. They look like little aliens when they come out. After a couple months they plump up and get cute.