what is wrong with famillies in 1st class ?
Nothing wrong with the idea, until you see some of the families and how badly behaved the children (or even themselves) are and go, 'oh'!
And could you seriously see a guard moving them? Any family that had no respect for others would be the ones that would refuse, or possibly worse.
Eurostar has Leisure First, which is in first class, but I think they reserve a section of FC - so while you enjoy the same service, it does keep them away from those who have paid more and possibly want some peace and quiet.