They were just hanging out. Donnie was watching something on his iPad, Leo was skateboarding, Mikey was making pizza, and Raph was trying to think of something to do. A portal appeared, and you fell out of it. They all looked at you

Donnie: Uhm... is that a child?

Mikey: Awee! It's adorable

Raph: Guys, most things we randomly meet are evil and try hurting us. Let's think this through

Donnie: What is a child supposed to do to us?

Leo: You'd be surprised... children can be so cruel...