if so - what was it like?

Couchette cars, with six beds to a compartment - bottom ones double up
as daytime seats, with the seat back swivelling upward to form a
middle bunk. There's a nice man comes round and sets up the bed for
you, and they come with a sheet/blanket and a pillow+case.

would you recommend it ?

There are worse ways of getting there, certainly. The only 'hassle' is
changinf stations in Paris, although this is not always a requirement
- check the details. Even if it is, it's only a couple of stops on the
metro, so not too bad.

How would it be with a 1 year old?

You may not be popular with your fellow travellers, but otherwise, why
not?

I've done the overnight Couchette train thing a few times - the one
I'm talking about goes in the day.

And I thought the TGV trains were modern / fast / sexy things, not the
40 year old sleeper trains?