This is Jaxon's trick that he does with Grandma Fay. Every time she props him on the pillows like this he starts grinning and straining to sit up. He'll be doing it on his own in no time.
Here's Leo practicing his super hero moves. He's basically obsessed with fighting crime right now. Every day (and some days more than once) he asks me when I'm going to make more super hero costumes.
And just for fun, here's an old, but adorable, clip of Jay being ridiculous.