Very odd. Wonder what could be interfering with the IR signal.
Any new toys in the house, such as remote control train, car. Any new devices, such as Laptop, Mobile Phone, any new lights - particularly Fluorescent / Energy Saving Bulbs.
Try to think of any object that has come into the room, which wasn't there prior to the trouble starting.
Have your neighbours experienced any trouble - could be worth asking, even though it may seem silly. I would expect interference to be very local, so not affecting neighbours - after all, remote controls do not work over a long distance, or through solid objects such as walls. Would therefore expect your neighbours to have no problems - but if they do, then some big interference is occurring, from something.
Try logging the times when the remotes are not working - see if there is any pattern to when you notice that they stop responding.
Seems odd - but as more than one remote is affected at the same time, then sounds like it is some sort of interference, rather than a IR receiver being at fault (though do check for spiders!)