There are currently NO licensed vaccines against malaria, or any other human parasite. The final results of an African clinical trial on a research vaccine should be known by late 2014, and hopefully it could be available by late 2015.
Antimalarials for children may be different in terms of drug type and dosage – weight is a better guide than age, and ( for example ) doxocycline is NOT recommended under the age of 12. Always check with your pharmacist, doctor and / or nurse. There is also advice available on various websites ( www.fitfortravel.nhs.uk ; www.who.int/ith ; www.nathnac.org/travel/index.htm ).
As for POSSIBLE side effects, they are too numerous to list on this Forum. For doxocycline and mefloquine they are most commonly “ non specific “ - like headache, abdominal pain, nausea, diarrhoea, vomiting, loss of appetite. These of course are far less serious than malaria. As my update has hopefully made clear, however, reported malaria cases have declined dramatically in the Philippines and most visitors choose not to take antimalarials.