Buy them these, obviously. Because all babies love Lord of the Rings. Or maybe all Lords of the Rings love babies. Anyway, there's no other logical explanation for all these appropriate bib and onesie jokes.
Lord of the Rings Bib, Fisher-Price Style
Here's a quickie to start you off. I laughed, anyway. You can buy one of these from Snazzy Stitches on Etsy. They cost $7.50, which seems totally reasonable.
My Precious Onesie
Let's ignore the hideously inappropriate background for a moment. Seriously, is there a better way to proclaim love for your child than drawing parallels between motherly (or fatherly) affection and Gollum's freakish ring fetish? No, I didn't think so. If you want one, the My Precious Onesie retails for $14.99 on Retro Baby Wear.
The One Ring Pop Onesie
Someone sat down and thought of all the possible "One [insert type of ring here]" jokes and came up with this. If you're sufficiently amused, you can get an adult version too. Get thee to Ript Apparel. Prices vary.
Lord of the Teething Rings
Oh look, it's another baby-appropriate ring joke. Etsy user ANimbleThimble made this one. I think the idea here is this: when parents are up late at night trying to comfort their teething baby they then think of this bib and laugh. You can't weep over chronic sleep deprivation when Tolkien's involved, am I right? What would Sam say?