Poisonous mushrooms, anyone?

Picture the scene - we're spending the day at a friend's house, and the kids (Darling Son (7), Darling Daughter (4) and their equally darling friend (8)) are playing over the road at an open neighbourhood garden.
Me: Lunchtime, guys!
Kids: We've already had lunch today, Mummy, we ate things from the garden.  We've had peaches and nectarines and mushrooms.
Me: Mushrooms?  Are you serious?!?!?!

Exhibit A: the mushroom in question

First I had to check they weren't kidding - they weren't.  Then I had to get them to bring a sample of the mushroom - they did.  Then us adults frantically got on the internet to Google 'poisonous mushrooms of Adelaide' - and there are plenty!
So the Poisons Hotline was called, and the mushroom in question described.  Verdict of the Poisons person was that it was 50/50 harmless/harmful identification, hard to decide over the phone.
YIKES!
How do my family get into these situations?!?!
After much parental wailing and gnashing of teeth (and consumption of lunch by 3 very un-bothered children) it was decided to 'wait and see', given that the kids had been over there for a couple of hours, and the Poisons person said that ill-effects would show 1-2 hours after consumption.

So we popped them in front of a movie and kept an extremely watchful eye on them for signs of fainting, vomiting, seizures, etc etc.  And by tea time it was decided that they had got lucky and eaten mushrooms that had sprung up from mushroom compost on the vegie garden.  Phew!