بسم الله الرحمن الرحيم
Parents use to train their children from an early age to adhere to the sunnahs of the Prophet.
Khalid ibn Dhakwan (tabi’i) narrated from Rubayyi’ bint Mu’awwidh (d. ca. 70) that she said:
The Prophet – salalahu ‘alayhi wasalam – sent his messenger on the morning of ‘Ashura to the houses of the Ansar saying: Whoever started [the day] not fasting, he should complete the day [not fasting], and whoever started [the day] fasting he should fast.
She says: Then after that we used to fast that day and make our children fast that day, and make woollen toys so when any of them cried for food, we would give him [the toys]; so they would be busy with them until the time of breaking the fast. [Al Bukhari; Sahih, Sawm: bab sawm al-sibyan]
Fasting on the day of ‘Ashura is not compulsory, but the believers were keen to encourage their children to grow in piety. As for fasting in Ramadan, children used to do it regularly.
‘Umar RA said to someone who was not fasting in Ramadan: Woe to you! Even our children are fasting. [Al Bukhari; Sahih, Sawm: bab sawm al-sibyan]
The Prophet salalahu ‘alayhi wasalam said:
That the father teaches good manners (yu’addib) to his child is surely better for him than giving charity of a sa’ in the path of God. [At-Tirmidhi; Jami’, al Birr wal-silah, bab ma ja’a fi adab al w-walad]
Source: ‘Al Muhaddithat – The Women Scholars in Islam’ by Mohammad Akram Nadwi, pp. 39.