Second/third chateau in Loire?

Chenonceaux is among the top chateaux of the Loire Valley. Chambord, with Leonardo da Vinci’s double helix staircase, is unique because it is surrounded by forest. Since the King of France took his furnishings with him when he moved from castle to castle, Chambord lacks any furnishings or interior appointments.
And that brings us to one of the most remarkable chateau in the Loire—Cheverny. With its origins going back some 700 years, Cheverny has been owned by the same family, the Huraults, for about 600 years. The owners were so loved by the local people that they protected them and their home from harm during the French Revolution. As a result, at Cheverny you can see a completely intact chateau with its incredible centuries-old furnishings, tapestries, and artwork.

More than a century ago, Cheverny was one of the first chateau to be opened to the public. Today, the family is still in residence and shares some sections of the castle with those wanting to see it.
This is rare in France, and a great opportunity to see the opulence of a luxurious chateau with an amazing history.

You can visit two châteaux in the Loire Valley and put (to my opinion) anyway Château de Chenonceau on your list. Besides this you can make a detour to Chambord just to see it from the outside. And finally go to Vaux-le-Vicomte because it’s just fantastic, not only for the looks but also for the dramatic story of first owner Nicolas Fouquet. Gives some variation too as most Loire castles are from the Renaissance period, as Vaux-le-Vicomte was built in Baroque style. So think with these three places you will have a nice package to enjoy.

Chenonceau is one of the greatest chateaux of the Loire. It has everything.

To your list I would add Azay le rideau, which is a comparatively small chateau, surrounded by a stream, and very charming. It has all the towers and turrets you want in a chateau but doesn't take as long to visit as the larger chateaux. It's my favorite, a little jewel.

Dont forget there is a Chateau right there in the center of Amboise. I found it to be just as interesting if not more than the others.

You’re right in Chambord being a little overwhelmingly large. I’d certainly not NOT recommend it, but compared to the intimacy you experience at the other Loire chateau it’s not my favorite. It felt much more akin to visiting Versailles or something, crowds included. That said, Vaux-le-Vicomte is probably on the same scale though higher on the quality. Given the straight choice I’d go with Vaux. However, they’re both big “sight-seeing” destinations with all the time and energy that go with that. Splitting the difference with a smaller chateau in Loire like Chaumont or Cheverny isn’t a bad idea either. Depending on your route, I’d also recommend Villandry or Azay-le-Rideau which are the other side of Tours, but easily accessible via the autoroute from Amboise.

Langeais has a beautiful midsized castle. When I last visited, (in 2017), there were reproductions of short kid-friendly plays from the balcony, complete with dressed up nobles, knights, and ladies. It was really nice, and all the kids really enjoyed it. However, I don't know if they do these in English- the plays were in French (my first language). They also did workshops and fun activities for kids.

https://www.loirevalley-france.co.uk/loire-valley-chateaux/chateau-and-park-langeais#:~:text=The%20Ch%C3%A2teau%20of%20Langeais%20is,architecture%20of%20the%20Middle%20Ages.

I would recommend staying in Amboise the day you return to Paris. We really enjoyed the Chateau Royal d' Amboise. It has beautiful gardens also. Chateau Clos de Luce, which was Leonardo Da Vinci's final home in Amboise, was also really interesting.

I also loved Amboise- the town, and both the Clos-Luce museum and the Chateau d'Amboise. Definitely worth a stop. Since first visiting in 1988, I've returned 7 times. It has definitely become undeniably more touristy recently, but it's still lovely!

Chambord was our least favorite of the 6 chateaus we saw last April (Chenonceau, Chambord, Cheverny, Clos Luce, Villandry and Azay). It felt big and empty and less interesting; we visited without any special event there.
Although I can't comment on your others stated options, I'd suggest staying in Amboise and seeing Chos Luce (and maybe Amboise if you have time). Clos Luce is small but it has a huge garden area that has life sized examples of Leonardo's inventions. Your 8 year old might love it! You can walk around the area and turn some cranks, etc. to make some of them work. It was beautiful in April and seems like the perfect choice for history and fun.

The other thought is that if you're going to be in the Loire, see the Loire. Since Vicomete is close to Paris you could hopefully fit that in on another trip.

I will be limited transportation-wise regarding a visit to Chambord planned also in June. Since It is being done as a day trip from Paris, I'll take train to Orleans train station to transfer to Blois on the TER. The bus in Blois station goes out to Chambord.

The same option for Chaumont from Paris Est unless I stay there a night or two. This entire area of the Aube River is famously historical connected with Napoleon in 1814 ,,,,Troyes, Brienne , Arcis-sur-Aube, Bar-sur-Aube, Chaumont in the defense of France against the Allies.

Chenonceau is my favorite, and i love them all, never tire of them. But, if i had to choose between Chambord and Vaux-le-Vicomte, i’d choose Vaux, hands down. It’s amazing and i think your 8 yr old will love it. My 11 yr old did. The Leonardo diCaprio movie, Man in the Iron Mask (good movie - highly recommend) was filmed there. It has a moat, stables, beautiful grounds and a fascinating history. It’s a castle that 8 yr olds imagine when they think of a castle. They also have a nice café there with good food, btw. It’s a great day trip from Paris.

The gardens at Chaumont are truly enchanting. It’s a great choice and it is between Amboise and Blois.

After Henry died, Catherine de Medici, his Queen, forced Diane de Poitiers, his lover, to swap Chenonceaux (which Henry gave to Diane) for Chaumont , Catherine’s chateau.

So including Chaumont is a nice historical connection.

(Late Note - Now corrected: Chaumont is what this should have said earlier. I have removed my erroneous use of Chambord, throughout. TY Wil )

Think going inside Chambord is worth doing for those interested in history. For those interested in the first place in the beauty of the castles to my opinion is the outside not to miss, it’s stunning and impressive. And just having a stop there is well to combine with the visits to the other castles.

Btw. was Diane de Poitiers not banned to Chaumont after the death of Henry II before she moved finally to Château d'Anet?