Lens, Paris, and Amsterdam sequence

I would definitely not backtrack to Paris, as it is bound to be significantly more expensive.
I would also say that going to Lens just for the Louvre Lens might leave you disappointed: the main gallery is a fantastically well-curated exhibit, but it is not large. Lens combines well with a few hours in Lille; would you consider spending the night in Lille?

Thank you balso, I am open to spending the night in Lille, for sure. Do you have recommendations for anything to see in Lille while we're there? I do have the RS France Guidebook (as well as the Paris one)

My daughter must be one of Giuseppe Arcimboldo's biggest living fans. She is so excited to see his 4 seasons all in a row "just as Arcimboldo wanted them displayed!" so I really don't think she'll be disappointed if that's the only thing we see.

Edit: it looks like under 3 hrs from Lille to Amsterdam on Eurostar

The Musée des Beaux-Arts in Lille looks great!

Lille is a fabulous city and the central old town and its architecture - both flamboyant and humble -- will richly repay a wander. Add in the Musée des Beaux Arts, wonderful restaurants and cafés, and it's a great stop.

I liked Lille a lot. In addition to the fine-arts museum, there's a museum of modern, contemporary and naive art. I missed it because its been closed for major work, but it's supposed to reopen before May.

I also really liked La Piscine, the art/ceramics museum located in an Art Nouveau swimming facility. It's in Roubaix, sort of a suburb of Lille so an easy side-trip.

The Louvre-Lens is not close to the Lens train station; I think it's about 2 miles away. I walked it, but that's probably not something you'll want to do with your limited time. There's bus service at least heading in the right direction, but check on its frequency for the day of the week you anticipate making the trip. The museum isn't right in a commercial or residential area.

A lot of French museums take part in European Museum Night, staying open (usually with free entry) on the designated evening. The date has sometimes been May 18. I think it was May 17 this year. A quick Google suggests the date for 2026 may be May 23. This is a way to squeeze in an extra museum or two, though the usual warning about avoiding highly popular museums on free-entry days applies.

A possible wrinkle is that museums sometimes plan to open a new temporary exhibition on Museum Night, which can mean part of the museum is closed in the lead-up to Museum Night for installation of the exhibition. Monitor the websites of museums you're interested in if you'll be traveling in May prior to Museum Night so you aren't disappointed.

Thank you Kim and acraven! I'll look at bus schedules and try to figure out what we're doing.