on like 1st season theme song when there at the park begging of there another kid who looks like he brendan age who is he? that i know of i never seen him on the show but he in theme song who is he?

He was the original actor who was supposed to play mark, but for some reason, he was fired, and they brought in Christopher Castille for the role instead. But, it wasa lready too late to change the opening credits, so they just left them the way they were.

You can see the theme song with the original actor here on my signature under Step By Step.