Jewish Leadership Council chief executive Simon Johnson and son Max did not let the train take the strain as they walked both branches of the Northern line to raise at least £3,000 split between Norwood and the Israeli Guide Dog Centre for the Blind.
They covered 29 miles over two days, finishing up at High Barnet on Monday.
"We slept like logs after 17 miles on day one," Mr Johnson said.
Boris Johnson has applauded Norwood's charitable work, describing it as an example of the difference between western values and those of the Islamic extremists who perpetrated the Paris terror attacks.
A record-breaking 1,350 guests attended the children and families charity's annual dinner at Grosvenor House in central London on Monday, raising £3.4 million.