It's not really about a pregnant woman getting kicked in the stomach though, is it? These things are never about the details, which are irrelevant.
In my view, things like this are happening more and more because people are becoming so very insular, concerned only for themselves and their immediate families and with that focus, unable (or unwilling) to read a situation properly and think before they say something. Everybody feels entitled to say whatever they like in whatever format they want... not everybody has restraint.
OP didn't do anything 'wrong', no - but said something maybe a little ill-advised and quite unnecessary that was taken the wrong way by somebody who wasn't interested and reacted in the way he probably always does, by shouting and swearing. Lots of people swear... I hate it, they do it anyway - gleefully, sometimes.
Probably the better thing to do would have been to leave the pool and speak to the pool attendant or manager and ask them to assess the situation. I'm not convinced it was a 'toddler' pool, not clear from what OP posted but either way, child had a right to be in it and OP's child also.
I don't know what the picking on Outraged is about, other people gave the same views, or some of them. Lots of bandwaggon posters about at the moment it seems.
Anyway, OP, I hope you are feeling better, it must have been a shock. You never know who you are approaching and what their response will be - better not to put yourself in their path if you can help it, I think.