The song was adapted and sang by Hartlepool sisters Olivia Crawford and Georgia Fletcher during Bradley's cancer fight to raise awareness and funds for the Bradley Lowery Foundation.
Bradley, from Blackhall, sadly lost his fight with cancer on July 7, 2017.
Speaking on the BBC Radio 4 show Soul Music today, Gemma told listeners about his fight with cancer neuroblastoma.
The Radio 4 show, which is now in its 27 series, looks to explore famous pieces of music and their emotional appeal.
She said: "Bradley was getting a lot of viral infections so I took him to the doctors as I wasn't happy with him.
"The next day Bradley went for a scan and that is when we found out that he had neurobalstoma.
"He was only 18/19 months old and he was extremely poorly, days away from death when he was first diagnosed.
"That night we got his last rites read off the vicar.
"I remember saying 'please God don't take him like this, give me another six months to make some memories. I don't want him to die in intensive care.
"At first he just lay there, didn't say anything, didn't smile.
"I remember the first time that he smiled. I got my phone out and said do that again Bradley. It was really emotional, happy time.
"He proved all the doctors wrong, he was a little fighter.
"The scan showed he was cancer free.
"It was December 15, 2014, when I got that news and that is the best news I have every got.
"I burst into tears and for once they were happy tears not sad tears.
"When I got home I say Bradley there are no more nasties in your tummy and he said; 'yay no more nasties!'
"He kept saying 'I kicked cancer's butt.'
"We had 18 months of pure normality. People going to work or school is a chore, but we just loved it. It was the best 18 months of my life."
Talking about her son's incredible personality Gemma continued: "He got the opportunity to be mascot for Sunderland and his character is just amazing, everyone loved him.
"When he got on the football pitch he just came alive.
"Generally we had to carry him everywhere or in his pushchair because he had long lasting nerve damage, but when he went on that pitch he was like that totally disappeared.
"Bradley was known for his smile and everyone who know him will tell you that the thing they remember is his smile.
"Two girls from Hartlepool came to us and said they would love to sing s song for Bradley and that they had permission to sing Smile.
"'Smile when your heart is aching', the words were so fitting as that us what we had to do.
"When we found out that Bradley didn't have long left and he was terminal we had to smile, even though we were absolutely broken, because there was no way that we were letting Bradley see us upset."
Gemma told listeners how Bradley's classmates sang the song as a way to remember him and even sang it at his funeral.
The words of the song have been altered to say 'smile little superhero'.
Gemma added: "He did hear that version of the song and he loved it because he thought he was a real superhero, which he was."