Depend where you go to. i have been finland late of march this year and lucky enough to see a strong northern light. you may join the "northern light" chasing day tour which will bring you to different area to see the northernlight. We have brought to the border to Russia in order to see the northern light. As you may need to stand and wait outside for long time, need to wear more. We wear all gears + the outer the tour provide. Still feel cold. To adult, it is fine but not sure if your kid is patience enough to wait.
If just stay in igloo hotel, wait and watch, it really depend on luck. We stayed there 4 days and could only watch it on last night.