The Children's Fitness Tax Credit gives parents a non-refundable tax credit to recognize the cost of registering children in sports. When the credit was first introduced, its cash value was $77.50 - the amount of the credit ($500) times the basic marginal tax rate (then 15.5%). The popularity of the credit among parents has led to it being enriched to $1000 in 2014 - a cash value of $150.
It's not that much money. Not compared to the Universal Child Care Benefit, which had a (pre-tax, admittedly) cash value of $1920 in 2015. Not compared to the Canada Child Tax Benefit, with a cash value of $1446. Not compared to the value of the Child Care Expense Deduction - worth up to $7,000 times the lower earner's marginal tax rate. But if one judged the importance of a tax provision solely by the number of academic papers written about it, it's one of the key aspects of the Canadian income tax system.
A partial bibliography of the literature on the Children's Fitness Tax Credit can be found at the end of this post. It's not a long bibliography, but it contains more academic papers than my recent disability tax policy reading list. Why all this interest?