I actually think that Teley has a point. It's like saying "She's young and Aboriginal". It sets the scene for judgement, even though it's clear that the OP didn't intend it that way. It might be easy for those of us who haven't been subject to 3 - 4 years of harsh judgements because of our age to be flippant about it. Perhaps not so easy for somebody has been subject to it day in, day out. There might have been a better way to handle it, but I understand what it's like having a raw spot rubbed the wrong way by somebody's seemingly innocuous words.
In any case, OP - I perhaps would try to strike up a conversation, too. Perhaps invite her around for a coffee and a chat while the kids play together, and maybe say something along the lines of "Is everything okay? I know we all have bad days, and lord knows 2 & 3 year olds can be challenging! How are you coping with it?" in a really non-judgemental way. You might be the friend she needs to be able to parent her children better.
It sounds like a really tough situation
Another great post, Tam.