kids pick up more than we know

My daughter asked me the other day Mommy if you have another baby which one of us will you sell? My jaw hit the floor and I said neither of you so then she says you will love us all the same? and I said of course I will. she was quite for a sec then said it is a good thing you don't want more babies and I said I do daddy does not want more kids and again she says but, why do you want more since we are so hard to handle? again I was speechless and I was unsure what to say but, it got me thinking kids in general pick up on things we would never even considered them to even hear, understand or know. but to think I would sell my kids if I had another one is something I don't understand where she would have gotten that. kids pick up on frustration and I can see the second part but any thoughts on the first statement?