Of all the purveyors of t-shirt irony, Threadless is my favorite. They let would-be designers submit ideas, which are then voted on. The winners get their design printed and sold as a limited-edition shirt.
The people-who-have-kids market must just be out of control, because Threadless is the latest in a long line of companies to begin producing children's products. Threadless Kids runs under the same principle as its parent: the community votes on kid-friendly designs, some of which are mirrored by adult versions (as in the photo at right). They're promising the same level of quality and service that Threadless is known for (I'll vouch for it, they're great and the shopping experience is a blast). Teeshirts in sizes 4 through 12 are $17, and onesies up to size 24 months are $20.
What I like best about Threadless Kids so far are the models—rarely do you see such a gathering of kids of all ages, looking like scruffy, cute, imperfect, real children. It's more like flipping through snapshots of my kids' last birthday party than looking at a catalogue. Bonus points for that, definitely.