Trip to Zilina or Zakopane between Krakow and Prague?

If you are considering the High Tatra mountains, I would opt for the Slovakian side of the mountain range because Zakopane seemed like a over-touristed urban resort when I was there. It is a city of 30K residents. The mountain towns in Slovakia such as Strbske Pleso and Stary Smokovec are much more appealing, although they are too far for a daytrip from Krakow ( 2.5 hours each way).
Not sure that detouring to the Tatra mountains will help get you from Krakow to Prague in a reasonable amount of time.
For hiking, you might also take a look at the Cesky Raj ( “Bohemian Paradise”) nature reserve which is an UNESCO World Heritage site near the town of Jicin

Thank you, Mr. E, very helpful. I think we can pay for transfers to get to Slovakia and then rent car to travel around for a few days. Our flights leave from Prague so we are kind of locked in there at this point. But there looks to be very fast direct train from Bratslavia or overnight, so we can end with a few days to say we say Prague before heading home. I know we're not going in the right direction, but sometimes I guess you just go where you're called.

Thank you,
Laura

So assuming we dip down to Slovakia for a bit, and rent car or use private transfers, any suggestions for great hotels to base from? I think the kids would love something with a spa, sauna or scenic, as otherwise we'll be in smaller rooms in two large cities (Krakow and Prague).

Strbske Pleso has a lake with several hotels with saunas and spas. Among them is the Grand Hotel Kempinski High Tatras, Hotel Solisko, Aplend Lake Resort and the Hotel Patria. Some were built as ski resorts back in the era when pyramidal architecture was popular and are quite unusual.

From Strbske Pleso, the well-preserved Renaissance town of LEVOCA is just a 30 minute drive.
Have a great Trip!

Thank you Kenko, Mr. E. The hardest part is deciding what NOT to do on this trip. This is my first, as well as my family's first, trip to Europe. We have typically done road trips in the US, camping and national parks. So my husband is quite used to travel that involves a bit of picking up and moving around. And keeping the kids moving through mandatory travel does tend to fight off any complaints of boredom and homesickness.

The reason to dip down into Slovakia emerged when considering where to go after Auschwitz/Oświęcim, and hoping for a more chill vibe. My husband got excited about seeing castles in north western Slovakia, the Sulov rocks, etc. We are still considering High Tatras, but they appear to be not quite as accessible. My husband is also wanting to get away from heavily touristed places for a bit. There is a direct train from Zilinia to Prague via Olomouc. There also appears to be a faster train from Bratslavia, as well as an overnight option, which would avoid losing daytime travel time (and give my kids another experience to check off!)

So much to consider! Thanks for all the ideas! So many alternative itineraries for future trips!

No apologies, this has all be great help! I am negotiating the IDEAL itinerary vs the reality of international travel, and factoring in three other humans with preferences as well as my own. Planning is part of the fun! Thank you for generously chiming in! I appreciate all input!

Also, my fam got on Atlas Oscura and identified this place as of interest. Sometimes you compromise for the sake of family!

https://www.atlasobscura.com/places/ruins-cachtice-castle

Yes, Orava, Trencin, Budatin, Strecno also of interest.

If we were to use DayTrip, can we ask for all these stops? We could spend a night in Zilina and use rental car for a day, but might be nice to have a guide take us to some sites en route to Bratislava where we can catch night train or fast train.

It sounds like a lot of good advise. one other stop not too far from Zilina is https://www.skanzenmartin.sk/ in Martin. Its a traditional Slovak Village. It gives you a taste of traditional Slovak life. You can get there by train and then bus/Uber. We have found Orava(Oravsky Hard) is one of the best castles in Slovakia, They have an english tour at a specific time during the day. If you are going through Trencin, also a great old town and another very good Castle experience. Train station is very close walk to downtown. Have fun. Check out the Slovak Spectator for maps and guide books.

Budatin castle (reconstructed I believe) is right in Zilina. There are 2 other castles which you can reach by train--Lietava castle and Strecno castle. I also went to Strbske Pleso one day.

These sites cannot be done in one day, you'd need more than 1 day to see these things, due to logistics.

I would say that Zilina is a good base for a few days (say, 3 nights) but there isn't much to see right in Zilina itself; you'd have to use trains to see a few things. I think a car is probably necessary in Slovakia to see multiple sites. I'd love to see Spis castle but the logistics didn't allow it.

If you're stopping for just 1 night, it's not really worth going there. You are not going to see much without a car.