Onsen and beach near Tokyo

I would be traveling with my wife and 2 kids to Tokyo middle of May. We are interested in Onsen and kids are interested in beach.
1) Are there a places near Tokyo that you would recommend? I can think of Atami that has both onsen and beach. Are there other options?
2) is it allowed to take 1.5 yrs old in onsen?
3) if you have any recommendations of reasonable ($150-250/night incld dinner) ryokan that would be very helpful

I can speak basic Japanese and can drive in Japan, have lived in Tokyo but it�fs been a while.

Thanks for your help

Enoshima also ticks the box. Very nice beach and an (expensive) onsen on the island.

Small kids are generally allowed into onsen, if they do not urinate/fecate into it. At some (mainly super sentos) they have small baby bath tubs for new horns who cannot yet control bladder and intestines.

Enjoy your trip to Japan!

Check out Hayama. Good beach, laid back atmosphere, a selection of hotels with and without onsen. You can get the train from Tokyo to Zushi, then pick up a rental car, with easy driving, handy restaurants and supermarkets. We took two kids, bit older than yours! and rented an apartment, and a car, and really loved it.

Check with each specific onsen/bath. I have seen some not allow entry to babies in nappies. For obvious reasons.