That mother was an IDIOT, period. Completely lacking in common sense. Possibly, she's just completely selfish and self-centered. I'm willing to bet that she was more concerned with her tan than she was with the welfare of her child. Seriously.
She let a four year old alone in a wave pool? I don't let my five year old swim without me nearby in the local kiddy pool, and when in the adult pool, waves or no, he gets a life jacket, and will, until he's proven to me he's an excellent swimmer, or tall enough to stand up and breathe.
Also, she sent her eight year old to look for the kid, after ten minutes? If I don't see my kids for ten minutes in a public place, I don't ask my teenaged sister-in-law to find them, I go find them myself, and quickly. These are things you just don't take chances with. Her eyes shouldn't have been off that child for a second, and if she couldn't see him in the churning mass, why would she expect lifeguards to?
This is a tragedy, and the women needs a stern lecture on priorities in life, and then be sent off to bear the consequences of her inaction, not rewarded with large sums of money, thus encouraging other parents to easily dismiss their responsibilities.
Judgemental? You betcha. If no one judges, then nothing is wrong anymore, and everything's OK. Her ignorance and inattention, directly resulting in her own son's death, is NOT OK.