I did a quick pattern search and came up with lots of fun, kid-friendly options that you could knit up in your favorite colorways. And with 25 colors of Rios and 32 colors of Sock, you've got a lot of colorways to choose from!
Great for Rios (try the felted projects in Merino Worsted!):
Neighborly by Jennifer Casa; On The Go-Veralls by Heidi Lehman; Granville by La Drougerie, project by Minelsa on Ravelry; Orly the Owl by Brooke & Beth; Felted Mittens by Molli Hartel; Harry Potter Scarf by Tangle
Good for Sock:
Cricket Pullover by Umme Yusuf, project by Snoozeecow on Ravelry ; Tjorven by Thorvalda; XO Mitts by Joanne Jongsma; Le Cardigan by Drougerie, project by Melanie-Math on Ravelry; Child's Button-Up Socks by Sara Morris; Holly, Ivy and Steve Three Christmas Ornaments by Rebecca Danger