Luckily, girls wouldn’t have anything to do with me in High School. I got into computers instead. When I choose a major Comp Sci was it. The point is its not so important that your kids do well in math or science per se as that they are exposed to it by their parents. Couple that with the expectation that they will not take the easiest major, or the one with the most hot chicks and they are well on their way to making good choices. You can’t force your kids into engineering or technical fields, but if you give them exposure to it early enough and make them take a few steps in that direction it will seem a whole lot less mysterious when they have to make their own choices. I for one never got past algebra 2 in high school and I had to take calc 2 and linear algebra twice in college.
Playing video games neither helps nor hinders your childs exposure to computers and science. Its a non issue. Getting them to build a PC, install an operating system or make a web page or even build a better mouse trap that gives them the sort of knowledge that leads to good choices.
Oh and it doesn’t hurt to talk about such people in a positive light either. Too often engineers and scientists are seen as nerds, even still.