A single mum celebrating her son's birthday at a park alone was taken by surprise when a family of strangers joined in to sing happy birthday.

Ashley Giselle Jeffords, 29, wanted to make her eight-year-old son James Carlton Cooley's birthday special despite celebrating alone.

So after picking up a cake the pair headed to the park last Thursday (Jan 2) for a low-key celebration under the gazebo.

As Ashley opened the cake and began preparing the candle, a father noticed James and asked his kids to join in.

Moments later, the family of three children and their parents surrounded James singing "Happy Birthday" and making him beam with joy."

Ashley who works part-time at McDonald's in Orlando, Florida, USA, said: "It was such a simple but powerful act of kindness."

"James was overwhelmed with happiness he had the biggest smile and kept saying how much he loved me and the day."

Ashley said the strangers' gesture was especially meaningful given her circumstances as a single mum.

She said: "As a mum, I do everything I can for James but sometimes I feel like I'm not enough."

"Seeing these strangers make his day reminded me that kindness is everywhere even when you least expect it."

The celebration concluded with James playing at the park and telling Ashley he had "the best day ever."

Ashley added: "That family didn't have to stop what they were doing but they chose to."

"They showed me how love and generosity can turn an ordinary day into something extraordinary."

"It's a memory James and I will cherish forever."