If your child holds a British passport and you're only planning to stay in Philippines within 21 days then the child doesn't need a visa. If you need to stay more than 21 days you can extend the childs visa when you are in Philippines or apply in Philippine Embassy in London.
If the child holds a Philippine passport then he doesn't need a visa.
Your husband and child (if holds British passport) can get an automatic visa at Immigration airport in Philippines when you can show to the Immigration officer that you're wife/mother holding a Philippine passport and marriage certificate, just present all your passport together when you arrive to the Immigration.
