London-Sorrento by train Any tips & can we put DS in taxi through Paris with no car seat?!

[EveryLittleBreeze]

Doing this journey in June with DH & MIL when DS will be almost 3. Am most concerned about the no car seat aspect of things as I think we'll need to get a taxi from Gare Du Nord to Gare De Bercy. Legalities aside, I wouldn't dream of putting him in a car here with no car seat but there is no way we can transport his 10 tonne Maxi Cosi with us by train just for a short taxi ride. Has anyone got any clever suggestion?

Hi, what about just a little booster seat? I think legally it is okay as it is a taxi. Or have you thought about getting the metro or RER? You might have too much luggage.