Get user id for SQL custom field - by: Connor Walsh

I'm using event booking for users to register their kids for summer camps. Each user has already entered their child's information on the website and this is stored in a database table. The children are linked to their parent via the current users id

My custom field is just going to be a select list with the children's names. I planned to do this with the SQL custom field type, with the query "SELECT child_name AS value, child_name AS text FROM #__child_master WHERE parent_id = $user_id"

I'm just not sure how to get the current user_id in that sql statement. If it were php I could just do JFactory::getUser()->id, but trying that in my statement didn't work.

Any ideas on how I can do this?

Thanks!