I think you need to at least think through every aspect of the arrangement. We did something similar when I was a kid and again with my DS so sorta been there,
Remember that 1st and 6th grades are not that far apart. My 6 year old has a 5th grade cousin that he plays often and well wit. Can your child separate the play from the discipline? What if they both get into it? Will you discipline them both? What about the younger siblings? How will he work into the play/ discipline equation?
Who sets the rules on where he can play, and what he can do? It really is a lot more to the mix than money and with his family as neighbors, you really want to avoid hurt feelings and other issues.
Remember that 1st and 6th grades are not that far apart. My 6 year old has a 5th grade cousin that he plays often and well wit. Can your child separate the play from the discipline? What if they both get into it? Will you discipline them both? What about the younger siblings? How will he work into the play/ discipline equation?
Who sets the rules on where he can play, and what he can do? It really is a lot more to the mix than money and with his family as neighbors, you really want to avoid hurt feelings and other issues.