Step-brothers Harris Bloom and Joshua Doyle, both aged seven, are best friends.
But the lockdown has been particularly tough for Joshua as he has been shielding with life threatening condition cystic fibrosis.
Joshua lives with his mum in Droylsden and the only child he has been able to play with is Harris.
All the family have been shielding to protect him.
To show his support for his best pal, Harris, also from Droylsden, has pledged to do something amazing during the lockdown.
He is running one mile a day for a week to raise money for the Cystic Fibrosis Trust.
Harris' mum Danielle Robinson, who is engaged to Joshua's dad Adam Doyle, said: "Harris and Joshua were two years old when they met each other. Even though they are not blood, they are brothers. They are best friends."
The idea came about when Harris and Joshua were given a £10 each by Adam's dad.
Harris tried to give his money to Joshua, but Danielle told him to keep it.
"I said why don't you do a run to raise money for the Cystic Fibrosis Trust?
"He said 'I want to do it'. He thought about it on Sunday and set up the online page on the Monday.
"A mile a day for a seven-year-old is quite hard. He said 'I want to raise £200', and it's gone up and up and up."
Harris' GoFundMe account shows he has raised £1,452 so far.
Joshua's dad Adam said: "It's just a lovely little thing. They are best friends. It's a lovely idea. On Sunday (Harris) said 'I'd love to do something for Joshua'. The last few months (Joshua) has had it pretty rough, not being allowed to do much. He's on 40 tablets a day.
"He takes everything in his stride. He never complains about anything. I've always seen the positive.
"He's a quiet kid, Harris is like the crazy one. They are the same age, but he looks up to him like his big brother. Everyone knows Joshua round here, he well liked."
To donate to the fundraising page, click here.
