I think he's three now? He doesn't show up very much, I guess because he doesn't fight. I think the Air Acolytes are often relegated to babysitting him when the older family members are busy elsewhere.
I recall Pema chasing him during the wedding because he was covered in food; I forgot that Meelo had grown up and that the little punk kid driving his mother crazy was the younger boy.
Here's a crummy clip that starts just before he shows up in the wedding scene.
Here's some pictures I have found of toddler Rohan, compared to his brother Meelo a few seasons prior:
Did I mention that pictures of him were a rare find?
I also remember him puking on his aunt as well in Book 2 or 3?