I'm a grandma of 3 (soon to be 4) under 5 years old. I've got 2 grandsons, and a granddaughter. I've made them each a couple of quilts in various colors/styles. I've also made the moms quilts with birth announcements/baby pics. I think everyone likes those the best. :)
I don't know really what the trends are. I make what I think they will like (and what I like). I did one with Laurel Burch Jungle fabric for my great nephew. That was such a beautiful print. For the boys, I did blue/yellow puppies, blue/yellow Snoopy & Woodstock, Pirates that had a lot of tan/green/blue/yellow, etc. For the girl, I did pastels, one with teal/coral mermaids. For the new baby (gender TBD), I hope to do either turtles or frogs and I will tailor it to boy or girl once I find out. I've done pinks/green stars for a baby girl.
I read that babies see black & white first. I only recently started liking black & white. LOL They look great with a few brights mixed in. I found a pattern called Love Bugs that is perfect for the B&W with color. I hope to make that one to keep here and use when they visit.