This is a topic you hardly ever see get tackled in rebirth isekai. The fact that you are effectively "killing" someone else and taking their body.
The best approach I've seen so far is "you are reborn as a normal child, and 'remember' your old life once you reach a certain age". Because, bare minimum, you are technically denying the parents their "real child".
Another approach I like is when taking over someone's body. It's someone who was about to die or just died instead. This way, the character is not really killing anyone, as much as taking an open slot. This does however create friction with their previous loved ones.
Still a weird topic to handle any way you look at it