Looking for suggestions and realistic expectations

My son (7) is really starting to get into astronomy and science, which I want to encourage as much as I can. The problem... We're within 10 miles of New York City, bortle 9, with skies as dark as bortle 5 in somewhat reasonable driving range, but the ideal setup would still be useable here at the house for nights when we can't take a trip.

Does anyone have any experience with using light pollution filters in such bright skies? Would they remove enough of the light pollution that he'd actually be able to view more than the handful of stars that are visible to the naked eye here?

And if there are filters that can make this feasible, is there anything I should know about minimum/maximum aperture or other aspects of telescope design that I should be aware of in a heavily light polluted environment?

Thanks!