Stephen Harper continued touting his low-tax campaign message Sunday by announcing that a re-elected Conservative government would create a $500 fitness tax credit for adults -- but after the budget is balanced by 2015.

He also promised to boost the children's credit from $500 to $1,000, a change also to be enacted once the government gets back to balanced books.

Earlier Sunday, it was reported that the children's credit would take effect in a Tory government's next budget. However, the Conservatives later clarified that both credits would come into effect when the government erases the budget deficit, saying there was a mistake printed in their campaign literature.

"A re-elected Conservative government will enact both of these measures before the end of our next mandate, because our approach is clear -- when we can afford it, we will lower your taxes," Harper said, while children practiced martial arts behind him at an Ottawa gym.

The children's fitness tax credit would cost about $145 million annually, while the adult credit would cost about $275 million per year.

A panel of experts will determine the activities that qualify for the credits.

"Canadians said yes when, in 2007, we brought in the tax credit for children's fitness and athletic and sport activities," Harper said. "It gives a tax break to hard-working parents, while providing an incentive for our children to develop healthy lifestyles from a young age."

The delay for the credits mirrors a qualifier in an earlier campaign promise made by Harper. Early last week, the Conservative leader proposed an income-splitting measure that would allow eligible families to share up to $50,000 of their household income for tax purposes.

But as with the adult fitness credit, the income-splitting measure would not be brought in until the budget is balanced.

Sunday's campaign event was held at an Ottawa gym frequented by a number of MPs, including Conservative Pierre Poilievre. Over the weekend, a number of campaign signs belonging to a Liberal candidate running against Poilievre in his Ottawa riding were vandalized. Someone had used black spray paint to draw crosshairs over candidate Ryan Keon's face.

Conservatives denied that their party was involved in the graffiti, which Harper denounced at Sunday's event.

"Defacing other candidates' signs is not acceptable for any campaign," Harper said. "Our campaign does not have the time to do that, we have enough to do to get our own signs up."

Despite the negative development, Sunday's affair was largely light-hearted. At one point, Harper and his wife, Laureen, held padded shields as kids practiced their martial arts moves on them.

The Conservative leader and Poilievre also played a game of ball hockey with a group of children at a local park.