Which airline are you flying with? We flew BA lately but pre the current restrictions. Our experience:
Call the airline in advance and discuss everything. They will be willing to help. But realise that everything they think will happen in theory may fall down when their disability policies are tested in practice. I'm certain I saw something on the BA web site about child seats and specifically ones for disability so I think this is covered but if you discuss everything in advance on the phone they put it on your booking notes so you have more confidence that when you turn up at the gate with it they can't say you can't take it.
We explained about drugs/food and got a note added to our booking to say we were allowed an extra item of hand baggage for her drugs, milk etc. The airline (rather than France immigration) required a note from the consultant to confirm this. I carried a big folder with this, medical history, meds, prescriptions, medicalert details etc. Re: meds, France allows in any prescription meds as long as you have the prescription with you and carry no more than you would reasonably need for the duration of the trip.
Nowadays, you will need a doc's note to specifically cover the milk and other food. Actually, I'd just put the meds you are needing in the plane in your extra hand luggage and check the rest: anything in a sealed container where they can't see through from side to side is still a no-no; you may get it through with a note but you might have to call a security supervisor to do so. A friend travelled recently and they made her throw away all the baby food (fruitipura etc) because it was prepacked. Home made stuff seems to get through - possibly I'd best not make any comment about that .
BA in theory runs a separate checkin for disabled passengers. In practice we got to Gatwick and there was the queue from hell and no disability checkin. There was another wheelchair passenger stranded so I barged to the head of the queue and embarassed a checkin guy till he shut the checkin for us! At this point you should be able to get a "wheelchair escort" Even if you don't need one physically, they know where all the lifts etc are and in some places you can't get through without their pass code (not anywhere I've been in the UK but in Bordeaux Merignac). I think you may have to book them in advance but mention to checkin person.
Because the buggy isn't physically a wheelchair, they x-ray it at the bit where you walk through the scanners and ours is fairly heavy (just a standard Mountain buggy but still), don't know what yours is like but be prepared they may make you haul her out for that.
At every stage (checkin, gate, plane) I had to explain again that the buggy was a functional wheelchair and we had to take it to the door of the plane and then arrange to get it delivered to the door at the other end. Everyone was OK with this till we came to board the plane then I got a lot of "No, madam, it's a pushchair so you pick it up at the carousel" nonsense. No amount of prior arrangement (and I did LOADS) will get you past this argument. The person you have to convince is the Purser on the plane because the arrangement to deliver the buggy to the plane at the other end is made by the captain radioing ahead. So if the stewardesses are on side (and they will be when they understand) you are OK. It's a bit different going back because Gatwick baggage processing means that wheelchairs have to go in a separate compartment in the hold and so you have to convince French airport staff as well as cabin crew. None of the above applies of course, if you have a wheelchair that looks like a wheelchair. It's just if it looks like a buggy that they try to treat it.... like a buggy. Stick to your guns anyway, it can be done.
Oh, and again if you have buggy-as-wheelchair, on the way out the captain radios France for the wheelchair escort, the escort turns up and sees no wheelchair just a bunch of people with buggies (and seriously odd offspring but that's their problem, right?) and so wanders off again and you get stranded in that bit of the airport, unable to operate the lifts. Do not let this happen. Grab him and don't let him get away!
What else?
If you arrange with the airline in advance and put a note on your booking, the checkin staff should reserve seats for your entire party sitting together which makes the whole thing a bit easier.
You don't all have to board at once. They board kids first to get them out of the way but we boarded self, DH, baby first and DD1 and carer came on the plane last of all so the amount of time DD1 had to sit still was absolutely minimised.
Err...
Oh yeah, food import. As far as I could find out from the relevant ministries, embassies, you can import pretty much any food into France with the exception of meat and meat products which still are subject to unjust BSE restrictions. Dairy or dairy substitutes should be fine. We took soya milk, some very specific cheese, fajita seasoning, all sorts! But we also did a bit of research on what we could get out there from what supermarket so only carried 2 days' supply. Note that France has not signed up to the EC food labelling directive so all the allergens may still be hidden in words like "arome" and "saveur".
Er...
I've probably missed loads.