Peloponnese Roadtrip spring

With just five days it may not be worthwhile to split your time.

There is plenty to do in and around Nafplio to keep you occupied for 5 days.

Check out the best website for Nafplio and you'll be amazed how much there is to experience in that part of the Argolis.

https://visitnafplio.com/

Would like to stay in quaint small town

Nafplio being a quaint small tow,n I agree with Tommy, stay in Nafplio longer and explore the surroundings from there.
The only criticism I have to make of Nafplio (old town), but this is my personal opinion, is that's a town dedicated to tourism where there are only 150 permanent inhabitants.

Here is a map where I have drawn lines to some places easily accessible from Nafplio

https://www.google.com/maps/d/edit?mid=1kFRC74X_9PHcQ_3FNY62F_tURD34mLs&usp=sharing

The first 10 miles along the coast towards the west to Lerna are uninteresting, it is much better after continuing along the coast towards Tyros.

On the east side I find Tolo particularly ugly with its seaside "resort" buildings, it will be much more in a "quaint style" if you continue further, for example to Candia or Iria

On the way to or from Nafplio consider stopping at Corinth. There is a huge fortress at Acrocorinth with 360 degree views over the countryside. Also Ancient Corinth and the canal.
Here are a few images.
Nafplio https://www.flickr.com/photos/stanbr54/albums/72157632094108982
Nafplio 2024 https://www.flickr.com/photos/stanbr54/albums/72177720319228274

Corinth Area. https://www.flickr.com/photos/stanbr54/albums/72157711755443483

I can tell you from experience that kids that age want to see stuff that is either fairytale in nature or historic while still being freakishly large.

In this case, you have the theater at Epidaurus, Palamidi Fortress, Corinth Canal, Corinth Ruins, Argos Castle, Acrocorinth.

Personally, while it's the obvious choice for adults, I think Mycenae is probably kind of dull for kids.

Kids also love swimming but first week of April is too cold for that (or maybe not; kids are weird that way).

I mean, just thinking geographically rather than peninsula-specific, you could easily add Delphi to this and while you're up there visit Hosios Loukas and / or Arachova. Maybe drive to Delphi via Nafpaktos or take the train to Kalavryta from Diakopto on the way.

Stay the night in Galaxidi. That's the kind of place you could let the kids run off and explore on their own.

If you decide visit Delphi, I also like the idea of staying in Galaxidi. It's a small, quirky town and fun to explore. We liked our stay at Ganimede Hotel. The are proud of their Award Winning Breakfast and have a Sea View Apartment that would be nice for a family.

We liked Pilos/Pylos alot - especially our stay at Karalis Beach Hotel. It's right below a castle that kids might (or might not) enjoy exploring. Swimming near the hotel is really nice but in April, it's likely to chilly for that.