You could call a gas safe registered engineer and get the fire serviced if it has not been done within the last 12 months. The engineer could then advise you on what the problem is. if just pilot needing cleaning or the electrode needing adjusting then this should be done on the service.
He will also check the chimney is clear and then do a spillage test to make sure the fumes are going up the chimney safely.
For the outlay of money you have to spend your family are safe.
Anygasman
December 2009