It completely weirds mothers out.
Here's why...... It denotes that you somehow love my child in the same fashion that I do. And that just is laughable and isnt even possible. So it really ends up making you look like an asshole.
On a weird-o-meter, if you have no children of your own and the child lives with BM, that would be a straight up 10.5!
If you have your own children and BM has custody and/or is a very hands on mom, ranks another impressive 10.5. Why? because you should know better not to lie. No one believes you. No one loves anothers child the same as their own. You are just saying it to sound good to others but it has the opposite effect. People are often left wondering what you poor kids must think. You may treat them as your own, but make no mistake, you do not love your husbands ex's children the same as BM does. Creeeeeepy.
If you have children or no children of your own and you are helping to actually raise the child/ren, mom is gone....dead, I can completely see how someone may adopt this attitude. Some still may not believe it, but it is sweet. And the child is probably happy. This doesnt register on my weird-o-meter.
What say you?