"these are mine"

i passed by a woman on the street this morning who was with her kids talking to another woman. these women apparently had not seen eachother in quite some time since the kids looked to be about 5 years old. referring to her children she says, "yeah, these are mine!" as if she was talking about a pair of jeans or something. does this mean that she has another set of kids somewhere that aren't hers? could the other woman have possibly thought that the other was a 40 year old babysitter? what kind of sorted past did this woman have that it required confirmation that these children were in fact hers??