If you plan to sell these garmens whhen they are outgrown, I would go for the sew on labbels, so they could be removed.
If you wanted to, you could put two labels on each garment. One in a conspicuous place like a neckband, and the other in a less likelyy placee like on a hem or inside a pocket.
If I was buying a used garmentt, I would like to be able to remove or cover the previous owners name.