I've visited Paris.
I've traveled with elderly parents.
I've traveled with friends in their early 50's with knee problems and friend in late 50's prior to TWO hip replacement.

I'd take taxis.
Not that expensive within Paris.
In my opinion, well worth the saved time, pain and to enjoy the view above ground as you go from one place to another.

The RER station at Denfert-Rochereau is equipped with elevators.

The choice of taxi or bus is a cost/benefit equation that each person solves differently.

I think we'll probably take a taxi hope it's not raining when we leave the restaurant! Last time that happened there were no taxis to be had, even when the restaurant called for one. Not a good end to an otherwise excellent evening.

It is well known that taxicabs in every city, town, and village are water-soluble.

Have a good trip!

...or to some, merely Wicked.

I know, I know, I have Elphaba on my brain.

Underhill...if you are trying to avoid stairs, you can take the Roissy bus and then the 27 to the Les Gobelins stop for Petit Marguery.

Sounds like a good plan (again, I think!), Ron, although I think we'll stick with a taxi rather than the bus.

Definitely do not count on the metro's to have working escalators or elevators..just too many chances of maintenance shutdown's etc...or particular levels might be locked out so you can't get to the one you need...I used the busses a lot on my last trip and think they are a better option for folks with walking difficulty...There might be a couple of steps but the rear doors have a platform that lowers to allow wheelchairs to get on board and that might be an option to ask for in case a couple of steps are too much...Plus, the seats in the front of the bus are designated for folks like old people, crippled people, or pregnant people..in other words, folks who need to sit down rather than folks who want to sit down...So it ought to work and esp in off-hours..no rush hour...Taxis within central Paris can usually get you back to your hotel for $10-15 US...
So that is an option as well...And if the parents can walk they should walk before the trip to get in shape for it...It will make it much more enjoyable for them once they get to Paris..and of course, really good walking shoes regardless of the transportation choice...

Most of our short trips in central Paris cost us about 5 euros or less. It was money well spent when we were tired of walking, wanted to get somewhere quickly, or needed to change before dinner and evening activities.

Taxis and buses are slow, so be sure you allow plenty of extra time for everything if you plan to use them.

But, a lot faster than walking!

I think I'll put this here, since the thread title is peripherally about limited mobility. The RATP schematic bus map (which is otherwise useless unless you know exactly where you are and exactly where you want to go) and the bus map with streets have keys along the edge showing which bus lines run wheelchair-friendly vehicles.

Schematic, key at bottom:
http://www.ratp.info/orienter/f_plan...aux&fm=pdf

With streets, key at left:
http://www.ratp.info/orienter/f_plan...eur&fm=pdf

Don't forget the boats which can be a very pleasant way of getting around, and are generally pretty accessible.

There are times that buses can get you closer to where you want to go with less stress than the metro. They may or may not be slower over all. We don't have a lot of appointments to make on time when in Paris anyway.

They all have advantages and disadvantages.

The Métro is fast, immune to surface traffic, and serves the city quite well. However, it is not very scenic, it can be crowded at rush hour, and it involves walking up and down lots of stairs.

The RER is like the Métro, except that it is faster and serves fewer stations, with longer waits between trains.

The bus is scenic and has far more routes and stops than the Métro. However, it is slow and very vulnerable to surface traffic, it can be very crowded, and you need a new ticket if you change from one bus to another. It's also a much bumpier ride.

The Batobus is scenic and leisurely but serves the city very poorly indeed, with only a handful of stops, all on the river. And it's not part of the RATP, so you have to use special tickets that are not cheap. It's basically useless for transportation unless you are very lucky indeed.

Walking is free, extremely scenic, unaffected by traffic, uncrowded, and serves every single point in the city without exception. However, it is tiring, very slow, and requires that one be good at walking long distances.

Bicycles are scenic and fun, and moderately fast, but they are vulnerable to traffic, and one must constantly get on and off the bike, as intersections with other vehicles and pedestrians are legion. Bicycles also require that you do something with the bike if you take a break, which is easier said than done.

Cars are very comfortable and can go from point to point, but there is no place to park them, and in heavy traffic it make take several hours to go only a few kilometres. They are very expensive and aren't very practical overall. They are not the least bit scenic.

And so on.

I think that a mixture of all the means of transportation is finally the best advice Though in my particular situation most metros and many buses (in Paris or everywhere) are not useful and I have to rely too much on taxis. But I still try to mix when I can, sometimes to save money, others time..and others just for my own mood

<i>The bus is scenic and has far more routes and stops than the M&eacute;tro. However, it is slow and very vulnerable to surface traffic, it can be very crowded, and you need a new ticket if you change from one bus to another.</i>

RATP is changing the ticket method so that you can make transfers within a stated period of time on the same ticket. I don't remember when this is going into effect.