Who cares. If you worry about this shit too much you're just causing unnecessary anxiety and bringing up your children in a bubble just stops them from developing a necessary immunity to germs.
Sure a keyboard has more germs that a toilet seat but Im willing to bet that the ones on the crapper are far more dangerous. And how is this surprising news anyway? When was the last time you disinfected your keyboard?
Yesterday, I do it most weeks, along with my game controllers, phone and pretty much anything else that gets touched.