30 years is a long time to remember a face. If my memory serves me, Marty never had any photos taken of him in the past, so his parents had to remember his face. If they ever noticed any similarities, they would probably put it down to coincidence because there is no way that their son could have been alive back then (to their knowledge).
English
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if someone had impacted in my life that much, I would remember after 30 years.
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Explain how your child was able to go back in time thirty years then.