Complex sentence: Whilst on drill, a boy hurt his head when knocked to the ground and when drill was over, Nicholson sought out the boy's family, made reparations and accosted his Colonel for knocking the boy over in the first place.
Split into simpler sentences: Whilst on drill, a boy hurt his head when knocked to the ground. When drill was over, Nicholson sought out the boy's family and mad reparations and accosted his Colonel for knocking the boy in the first place.