"The mother jumped in to rescue her child and went in again to retrieve the pushchair,"
I think I'd have abandoned the pushchair!
Thank god the baby wasn't hurt - we have the problem with high winds down here on the coast. I don't take DS out in the buggy when it's bad, I worry about exactly this sort of thing (except for us it would be the road, not a lake).
Last year, my friend got hit by a massive gust of wind as she turned a corner - her buggy flipped over with her DD in it - thankfully she was ok (barred a bump on the end) but how scary! And that was a Phil and Ted E3, not a lightweight stroller or anything.