This is weird. But I totally agree with HauteMama.
We shouldn't judge people on their feellings, it's something we just have no saying over. They are adults and are free to act how they like as long as they don't hurt other people.
But I do have to say, I do find it weird that they choose to act on these feelings. They will never be able to return to a 'normal' mother/sun relationship after this if it doesn't work out. If they would ask me I'd say they made a HUGE mistake. But if they choose to risk this it is their choice.
Personally I find the idea a bit sickening, but there are many things that people around the world do that I find sickening