I dont know about the beaches in LA, mainly because they're always overcrowded during the summer, and there is not a bunch of things to do for the young kids.
If you're willing to drive down to Orange County, there are tons of beaches that offer an area for swimming and other areas for exploring [tidepools!!!] here's a link that should offer you what other people have to say about the beaches I usually visit.
LINK
If you're willing to drive down to Orange County, there are tons of beaches that offer an area for swimming and other areas for exploring [tidepools!!!] here's a link that should offer you what other people have to say about the beaches I usually visit.
LINK