But none of their stunts have been quite as hair-raising as their last one.
"I said he could cut or shave my hair however he wanted, knowing he'd never used clippers in his life," said Tim.
"We've done a few things for the NSPCC now like climbing Mount Snowdon and Scafell Pike, but none quite as crazy as this."
They have raised around £200 so far and are appealing for more people to sponsor them.
Billy said: "I got the idea of the style I wanted from an old photo of him and then someone said about dyeing it pink.
"I took him from baldylocks to Goldilocks to the Pink Panther and we had a great laugh doing it all for charity."
His brave dad said some of his taxi customers have likened the new look to Elvis.
"I think he did a pretty fantastic job," added Tim.
"This was Billy's first time with scissors and dye and he loved doing it, bless him."
He said he wasn't scared before the stunt and quite likes his striking new look.
"My boy calls me Pink Panther but, I had a regular in my cab this morning who called me Pink Elvis," added Tim.
"I'm a Elvis fan, so I like that one."
For more information on the fundraising, visit virginmoneygiving.com/TimSharp or to see the challenges on Facebook, visit facebook.com/timsharpandnspcc and the secure donation page is virginmoneygiving.com/TimSharp.