Well, she fell unconscious immediately after pushing out two kids. It's not too crazy to think that during that time she was in enough pain not to know exactly what was happening. Also, as mentioned, the doctor was paid off so he could have smoothed over any confusion she had. After all, he delivered her kids, he's a professional, of course she would trust him.
Also, as for the prince not checking to see whether the kid's DNA matches the mum's, well, who expect someone to be as heartless as to snatch up their own sister's child? Also, if it weren't her child, he would expected others to come forward claiming so, but no one did.
As for the mum not noticing the change in children, it actually isn't that surprising. The clothes might cause some confusion, but, the likelihood of a child being suddenly switched out with a doppelgänger would be exceedingly low. Also, as for the personality, kids are moody, they can act completely different from one moment to the next. Besides, it's only been like one day and she still thinks he's a little "traumatized" from getting lost.
(Not trying to hate on your comment or anything btw. I do agree that the number of exceedingly unlikely occurrences are kind of weird.)
This manhua is a piece of junk . As soon as I finished second chapter,I became sure of it. It'll be a painful read if you are gonna use your brains. I shut off my brain after 2nd chapter and enjoyed it thoroughly. You are never gonna get the answers that you want so it's better if you drop the questions or better,drop the manhua.
Dude the sister n mom r pieces of gold-digging trash, wtf for real right now...did she somehow fail to notice she had twins & just never reported the other twin kidnapped or missing?! n y in hell did the father not do a dna test on both the mother n son 2 c if she was lying...& HOW just HOW! do u not notice ur sons clothes & personality have obviously changed & not suspect tht the twin could've come back n switched places... There r so many thing that were not explained tht the characters come across as idiots! So many holes in the plot so far like damn... Σ(っ°Д °;)っ