In Jesse by Gary Soto, what favor does Abel ask of Jesse? Why does Jesse do it?

Abel asks Jesse to take care of the baby so he and Maureen can go out.  Jesse agrees because he wants to help his brother.

Jesse and Abel are on their own.  They moved out, and both started attending junior college even though Jesse should still be in high school.  At the junior college they could be on their own and take care of each other, and not worry about living under their volatile stepfather’s roof.

Jesse and Abel are both taken with the landlord’s daughter Maureen, who already has a child.  However, she is much closer to Abel’s age than Jesse’s.  She likes him but still thinks of him as a kid.  Abel and Maureen hit it off.

Then Abel pulled me aside and said, “Jesse, can you do me a favor?”  I could smell his cologne and soap, and a little of Maureen’s.  I could see he didn’t want to ask.

“Can you take care of the baby?” (Ch. 15)

Jesse can tell that Abel feels bad about leaving him behind, but he and Maureen are going out with Leslie and Glenda, and Abel doesn’t want Jesse to tag along.  Jesse understands, however.  He appreciates that asking him to stay behind is hard for Abel.  He doesn't want Jesse to feel left out.

Because I loved my brother, and because it was their turn and not mine, I nodded and said I would be happy to take care of little Larry. (Ch. 15)

This is an example of how Abel and Jesse are slowly growing apart.  Abel is older, and wants to do more adult things.  As independent and mature as Jesse is, he is still the younger brother.  Tagging along with Abel is not always going to be an option.  The brothers are going to need to go their separate ways soon.