Too bad, Leo, you're a good kid. And Steve wants you to know that. "Let me know if you ever need to peel him away from the screen. I think I'm pretty good at that." He's also physically rather strong, which is why.

Mostly, he just thinks it's nice that they get to be here together. Two brothers. Steve's is here, too - he considers Bucky his brother. But. It's kinda not the same, so, he can channel his happiness for the turtles instead.