There is a calculation called "business use of home". You take all expenses for the house such as your mortgage interest, property taxes, heat, hydro, water, and I put my cable and internet into that one too and any repairs you did to the property that benefit the daycare and add those all up. Then the calculation involves taking the amount of space used for daycare over your total size (include basement here in total if you use it) times the number of hours of care you provide and I add a couple ie one either side for prep and late arrivals/clean up as well as a divided by 24 and if you only do weekday care you need to then multiply by 5 divided by 7 then you factor in the house costs you added up and that gives you the business use of home cost to claim.

Ok so what I wrote won't help you because it is too confusing I know. The actual formula is in that daycare booklet on the revenue canada website. But what you need to know to do the formula is:

total of the house expenses
total square footage of your house including basement if you have a playroom down there
amount of square footage you use for daycare (play, eat, nap,)
number of hours of care per day (time first arrives till last leaves plus 2 hours for prep/cleaning)
number of days out of 7 you do daycare (so 5 for Monday to Friday care)