PIL live in France and we visit them once a year for a fortnight. Previously we have taken our own car seat on the plane but we are going by train this year and they are picking us up from the station. They are willing to go and buy a seat that is suitable for DS to use but I don't know anything about the regulations regarding seats in France and neither do they!
DS will be 2.5, he's currently 91st centile (13.5 kg) for weight and 75th for height(88cm).At home he's in a Izi combi isofix RF.
Any recommendations?