plants v zombies ps3

Here is how to make a child's account:

http://help.ea.com/en/article/how-do-i-set-up-an-origin-account-for-my-child/

If you need further assistance EA Support will be the place to go as we can't do anything with accounts here on a public forum.

http://help.ea.com/en/contact-us/new/

When we try to play PvZ online it comes up with a message 'Online service is disabled on your Sony Entertainment Network' is this a EA or Playstation thing.

Sounds like it'd be related to your PSN account.