UKC

Looking for destinations recommendations for end of March/April/May for 3-4 weeks, would love something similar to Railay: family friendly, safe, warm & calm sea, beach, easy climbing, things to see... 

Not Europe. Long haul is ok.

Railay ticks all boxes apart from the weather - gets much too hot in April ((( 

Thanks in advance!

South of France  or Kalymnos would be the obvious suggestion but you want not Europe. 

Some of the stuff in Western Australia may be a good fit too. 

Have not been to this place yet but I think it ticks all of your boxes except the climbing options are probably good for no more than a week:

https://www.mountainproject.com/area/116212536/loreto-area

Could combine with another place in Mexico.  This was excellent (no beach though):

https://www.mountainproject.com/area/106121301/pena-de-bernal

Then there's the obvious El Potrero Chico.  Or you could focus on beach and/or cultural tourism stuff after that.