The first duty towards children is to make them happy. If you have not made them so, you have wronged them. No other good they may get can make up for that.
Bio: Abraham Isaac Kook was the first Ashkenazi chief rabbi of the British Mandatory Palestine, the founder of Yeshiva Mercaz HaRav Kook, Jewish thinker, Halakhist, Kabbalist and a renowned Torah scholar.