Mont St. Michel vs Versailles

Mid Sept is still high season in France, so expect both sites to be crowded, especially at midday. Because MSM is so far from Paris, any day trip would have you arriving when the crowds are at their worst, and leaving before you really had a chance to see everything.

Versailles would likely be just as crowded, but at least you can buy a timed admission ticket in advance and get there early in the morning (or later in the afternoon). And your travel time would be much shorter.

However, with only 3 1/2 days (how many nights?), I'm not sure I would want to sacrifice a whole day ( or more in the case of MSM) to visit either if them. Paris has so many places to experience on a short trip. But it's up to you.

It has been a long time since we were there, but I don’t recall anything at MSM of particular interest to children. The abbey church is quite austere. The way up is lined with tacky souvenir shops and over-priced mediocre restaurants. It looks great from a distance, but up close, meh.
3.5 days is not very long for Paris, itself. I suggest you consult one of the guide books with a title like “Paris with Kids”, and let them pick out some things that appeal to them. One thing they might enjoy (you, too) is the evening cruise on the Seine.

Versailles sounds better. MSMichel is wonderful and a place you should spend the night....but to me its a lot with 4 kids for a day’s visit. Save MSM for a another trip when you can reserve a room on their island early and enjoy that wonderful place. Versailles is an easy day trip on the train out of Paris and will be easier for your family.

We will be there for 4 nights, and I thought if we left mid day to MSM we would miss the early crowds and stay until closing and spend one night out that way. But if it’s not as cool as it looks maybe a trip to Versailles would be a better option!

With your children I would definitely lean towards Versailles. Once you have seen the chateau you can go into the gardens and rent bikes, which is a lot of fun! You can stop at the Petite Hameau, see the Trianons, and explore. The grounds are vast and it's really fun to find all of the hidden corners and wheat fields. You can also take a boat out onto the Grand Canal. St. Michel is nice but really far away and you won't get much time there.

It would be too short on the spot for your children to enjoy Mont St Michel after a rather long trip. To really enjoy the area between Brittany and Normandy, you would need an additional night (for example to explore around St Malo and Dinan, to sand yacht along the bay of Mont St Michel...)

My impressions of MSM mirror those already shared by Rosalyn, above. We spent a week in the region, had a car, and visited MSM for about half a day (2 adults and a 20 yr old nephew). It was ample for us. For me, the view from the distance was incredible, but once on the island, honestly, I could have been in Anytown, France...which certainly isn’t a bad thing at all, but hardly worth all the schlepping that would be required in your scenario. (Actually, my nephew now hardly credits MSM in his recollections but waxes lovingly on the hours spent eating oysters in Cancale that afternoon). I have visited Versailles three times, so I must confess to a slight bias. To my mind, it is the iconic palace that defined palaces for generations of royalty and so much easier to reach, and especially with your group. Younger kids might also like a break from history to run around gardens with ice creams. Is the KIng’s Apartment tour still offered? That made it very convenient and enjoyable. Safe travels and have a wonderful time with your family.

With so little time in Paris I would do neither. Versailles is a misery for small kids and it will be high season and crowded. I see nothing at all fun about MSM for children. The view of it across the fields day or night is stunning but there is nothing much to do there and it is a tourist trash nightmare except for the abbey itself which I would doubt most kids would find fascinating.

Versailles has nice gardens especially on days when the fountains run and they might enjoy the Hameau -- but I would rather spend the time in parks in Paris than make the trek and the palace itself is really jam packed that time of year.