If your sons are being coached in their league, you should check with the coach to see if it is time for them to move on to their own equipment, that is what the coaches are there for and, if they are observant, they should be approaching you regarding the same or, at the very least, they should be able to properly assess your children's abilities at this point.
From an age standpoint, and averaging 80, the ten year old is probably ready for his own ball as the sooner a bowler is properly fitted for a ball, the better the chances are that the bowler will not develop bad habits due to a poor fit. I would hold off on the 7 year old for awhile, keep an eye on his progress and, again, keep the lines of communication open with the coaches.