The pendants are made of 18k yellow gold and encrusted with diamonds in a chosen initial. And, as cute as they are, there's a reason you see them on celebrities and not on the moms in playgroup -- they cost $1250 each.
Even if you don't have a little one of your own (or if you're just not digging these particular pendants), she has loads of other options, but all are in the upper price ranges.