A Calgary dad is hoping a thief has a change of heart after his son's custom bike went missing from their backyard on Thursday.

Joshua Krohn said his nine-year-old son Dallin realized the bike was missing from their Bowness home when he got home from school Friday afternoon.

"He went to play outside and realized his bike wasn't there," Krohn said.

Dallin has achondroplasia, a condition that causes shorter bone-growth in his legs and arms.

The purple mini-BMX bike, worth between $250 to $400, had a modified seat and handlebars that had been cut to fit his proportions.

"It was a life-changing thing for him to have a bike that fit him properly," Krohn said.

"I mean, he went and got his own tools to take his training wheels off … and was riding around like he'd been on a two-wheeler his entire life after 10 minutes."

Krohn said he's had people step forward to offer to buy a new bike since he posted about the theft on Facebook on Friday, but he's just hoping his son's bike will be returned.

"We just want the bike found. There's been lots of generosity there to buy a new bike … we don't want a handout. We just want his bike back," he said.