I imagine he touched him really softly, gently, slowly, and left his hand on Marco's shoulder or elbow or wherever he touched longer than normal.
Y'know, like they do in dramatic soap moments.
Dang I love Ax. I hope the reprint survives long enough to put out Ax books, but starting with the first two of the series seems risky to me.
Also, I know second graders who read these books nowadays and get it. The material's kinda stuff we find questionable as adults, but let's face it - the vocabulary's pretty simple and redundant and you can understand what is technically happening in each scene. My cousins have been reading this stuff since third grade, the people at my synagogue have donated books and the common age group for picking them up is second/third grade.
The nice thing about the series is that while you can go pretty deep into it, kids from a lot of ages can at least understand the story. At least, that's my opinion based on the kids I know now reading it. Though I think getting the deeper messages aren't realistic for the younger grades... Even though I know I could and did in elementary school when it was coming out. (4th/5th/6th grade, not 2nd/3rd of course.)