My dad would introduce me to mathematics that was beyond what we were doing in school. For example he taught me how to multiply two digits by two digits when I was just learning the basic multiplication up to 5 x 5. Also our family trips were to museums and other places near by. When we were out he would be sure to teach us about the stuff that was there. At the amusement park, we were learning about the different forces long before we took physics. We also played with circits (batteries and stuff), chemistry sets, and my dads workshop (wood and stuff, he builds houses). The point is to try to make mathematics and science a part of daily life. By not separating math and science, you may make the activities a bit more interesting. Also you can find books on math projects (as well as science projects) for kids.
