Have your kids actually learned/mastered the concepts of multiplication? If they haven't, it does not really make any sense to already have them memorizing the facts. We won't even touch the concept of multiplication until November or December. Only after we've thoroughly covered the concepts (done all the things that others have mentioned) will we start memorizing our facts. Also, have they mastered 2's, 5's, and 10's? Those are the ones we start with.