It doesn't get much sportier than this track suit by Krawlers. The pants have built-in kneepads and the jacket has removable sleeves, just in case baby needs to flex. All that's missing is a headband and a pair of cross-trainers. Also available in green and pink. (Branding alert: The brand name is splashed big-time across the back of the jacket, so if you're wary of such displays...)
$35, Style Kid.
