North Wales Fire and Rescue Service said there was often a rise in deliberate fires during school holidays and the warmer weather.
The service has asked parents to be aware of what their children are up to over the half term break.
All the Welsh forces saw a rise in fires over Easter - with about 500 in south Wales alone.
Suspected fire starters, some as young as 11, have been arrested for deliberately sparking fires in south Wales.
In north Wales, 145 fires were deliberately set in March and April, including 62 grass fires.
Arson reduction manager Kevin Jones warned deliberate fires tie up crews, preventing them from attending life-threatening incidents.
"My appeal is directed in particular to parents and guardians," he said.
"Please try to be more aware of the whereabouts of your children and impress upon them the fact that deliberate fires endanger lives."
Parents in north Wales are being urged to help stamp out deliberate fires during the Whitsun holiday.