Usually I will check out Skyscanner and Kayak
But once armed with information don't forget to check directly for Airline 'promos' and also contact your local travel agent who may secure some additional benefits.
There are quite a few reputable agents who advertise in those freebie Pinoy newspapers like Planet Philippines
Some of those that have been used by members here with good reviews include PIC-UK (Philippine Islands Connections) and Crystal Travel
They can often offer similar prices with the benefit of additional luggage allowance or maybe better connection timings.
You may be interested to review yapta.com as it allows flight price tracking and lets you know when the price drops.
Most airlines do require you to buy a ticket for children over 2 years old.
Good luck
