His next challenge will be The Abersoch Half Marathon on October 4 followed by a run/walk from the foot to the peak of Mount Snowdon.
The 40-year-old who works in London Bridge, said: “The charity's drive, spirit and obvious love had me promising my support in minutes.
“It’s magic for me to be a part of the charity’s ongoing and continued success story and to help keep Freddie smiling.
“I hope to raise £2000 so please give generously for a worthy cause with a good heart. It will be nice if we can make a difference together.”
To sponsor David, please visit his JustGiving page