If your stopover is longer than 24 hours I don't think you'll be able to check your luggage through. But if it's less than 48 hours then you may be able to check it straight back in again at the airport (depends on the airline for the onward flight I think). In any case, moving luggage around in HK is as easy as it is possible to be (which is never going to be a breeze with 2 kids I guess). Trolleys are freely available at the airport and at the airport express train stations. It might be an issue if you have more luggage than can be fitted in the boot (trunk) of a taxi though.