Someone said that to me once, I simply replied "I don't think so."
I don't take the comment as anything about her and her kids - it wasn't a statement about her, it was a statement about me. If she wanted sympathy or cmiseration or something, she should have made a 'me' statement about herself, like "I envy women like you/without kids." But she didn't. She commented on my life circumstances, of which she knew nothing. I did think it was a nasty thing to say to someone such as myself. She might not have known I would rather I had kids, but it wasn't her place to comment on it with a value judgement.