Reincarnation

I'm curious about reincarnation after my niece told her mother she picked them as parents while she was in her mommy's tummy she was 2 or 3 at the time she said this she's 12 now. I asked my other sister to asked her son what's the first thing he remembers or if he remembers anything from being in her tummy and he said the same thing. He was 5. My niece and nephew live 2000 miles away and almost never talk and they are 7 years apart. I've read ages 3-5 are the best ages for them to remember, if this is true. Have you had any experience that made you question or believe it?