As recent west coast transplants, and then clawing to survive in my 1L year of law school (I am a 2L now, though to be honest, it isn't really any better), we lived in the Bay area for 7 months before finally making the hour journey to see the ocean. It was March, it was chilly, but we were dressed for it and the kids LOVED it. I loved it. I had no idea I would enjoy the beach but I did.
So if you want to go, just bring extra towels, clothes, old long pants, etc. If they get cold, they'll let you know and you can get them warmed up. Wading, digging in the sand, and running from the (cold) waves coming in is the fun part anyway

. (of course, it really isn't ever warm enough up here to swim for real in the ocean --imo).
If you've got a day to go to the beach, go. Even if its chilly. Unless its really windy. So windy that the sand keeps blowing in your face. That's just miserable.
(my 4 year old daughter just came in sad because her friend and family were leaving to head to the beach today and its only 57 degrees).