Well there are a lot of things to do here... well you can spend around 3 days in Manila to check the metro, Intramuros, Manila Ocean Park, and its malls and its nightlilfe.. you can take a day trip too to Corregidor.
then you can spend 4-5 days in Puerto Princesa city to check the Subterranean River and spend time in the islands of Honda Bay... then you can spend another 3-4 days to Boracay or fly to check out the Chocolate Hills and Tarsiers of Bohol island...
From manila you can drive to Subic to check the Zoobic Safari and Ocean Adventure.. this may be something a 5 yr old would appreciate. Or you can take a day trip to Tagaytay to have lunch on its restaurants that offer the scenic view of the Taal Lake. Tagaytay also has a number of spa facilities.
For Puerto Princesa (Palawan) there are travel packages that offer nature tours there which I am taking with 12 other friends 2 weeks from now. It includes a trip to the Puerto Princesa Subterranean River, which is the Philippines' entry to the New 7 Wonders of the World. Also it includes island hopping on Honda Bay. You may opt to see El Nido which lies also on the island of Palawan, they've got very good dive sites and resorts.
For Bohol, the Philippine tourism authority has a package that includes spending time in a dive resort, touring the island, cruise on Loboc River, and viewing the Chocolate Hills. You may also have a side trip to Cebu.
For Boracay, it is famous for its sugary-soft white sand beach and lively nightlife along the beach.
Since you're from the UK you would probably fly in through Manila. And from Manila you can take domestic flights to Puerto Princesa, Boracay, Bohol, or Cebu, while you can rent a car or take a bus from Manila to Tagaytay or Subic.