A "lawful excuse" is ANYTHING that the particular court agrees to beforehand, or circumstances beyond your control that arose without prior warning. You child care issues are not a lawful excuse unless you arrange it with the court prior to the court date. If you call them, they will probably agree to postpone the hearing. If you don't, the judge isn't going to consider your excuse an excuse at all, lawful or otherwise.
Not sure in Canada but in the US if you are not in Court that day you either need to be: in another court that day, in the hospital or something in that nature, your child care issue is considered personal and may not be a valid excuse