Um..... from experience... as others as said it will not work if it isn't SECAM compatible....One work around we did with our old UK set was to input the Terrestrial signal via a (French VCR), though even in that case the best got was a black and white picture with the sound.
Failing that anything
not input through the RF (co-ax) socket will probably be OK, e.g. the SCART sockets, HDMI, etc. If in the future the family do decide they want to receive French TV ( and there [I]is[/I some stuff worth watching,e.g. sports) one option would be a TNT decoder feeding the TV through SCAT/AV in. sockets. TNT boxes are at the moment readily available at the moment from most large French Supermarkets or DIY stores .. ....and finally, BTW whilst a using digibox is fine for Freeview, you really shouldn't ever be receiving "Sky" on one of their boxes in France......OK
PAL, SECAM & NTSC: Using a TV in France - AngloINFO French Riviera, in the Côte d'Azur (France)