A four-year-old US girl’s encounter with an elderly man during a shopping trip has led to an unexpected bond which has captured the hearts of thousands.

Mother and writer Tara Wood shared an account of their meeting to her Facebook page late September, saying she was taking daughter Norah to buy cupcakes for her birthday when the girl became inexplicably drawn to a fellow shopper.

"Her face lit up like the sun, she waved excitedly, and said, 'Hi old person! It's my birfday today!’” Ms Wood recounts.

"He was furrow-browed but his expression softened when he realised she was speaking to him. 'Well hello little lady! And how old are you today?’”

Norah clutches a framed photo of her and Mr Dan; mother Tara Wood takes a selfie with Mr Dan. (Facebook/Tara Wood, Writer) (Facebook/Tara Wood, Writer)

Ms Wood said the pair immediately hit it off, with Norah eventually asking to take a picture with the stranger – a request that Ms Wood said left her new friend, Mr Dan, delighted.

The photo, posted to Ms Wood’s Facebook wall, shows the pair embracing one another as if they were “long lost friends”.

Ms Wood has told CBS News that Mr Dan has credited Norah’s kindness with having helped “heal” his sadness and anxiety.

A series of subsequent encounters have been detailed in posts to Ms Wood's Facebook, with the mother-of-seven insisting Mr Dan is now "going to be part of our family whether he likes it or not (he likes it)”.

(Facebook/Tara Wood, Writer) (Facebook/Tara Wood, Writer)

She ends one of her posts by asking readers to ensure elderly people feel like they are seen and heard.

"Let's take good care of them and love 'em all up,” she wrote.

Ms Wood’s posts have drawn hundreds and thousands of reactions on Facebook.