Booking as far in advance as possible with the budget airlines or being prepared to fly at odd hours is usually the way to go to get a cheap price.

I do not envy anyone flying with a baby / small child on a plane. It dam hard. especially when it is a short haul flight London / Geneva and it gets delayed for a total of 3 hours. Two of which we were sat on the plane waiting for take off slot. No toilets, food, entertainment and a screaming kid.

Good luck.