In order for the children to accept this good attitude and behaviour, it is essential to make that beloved to them. Love cannot be instilled by means of force and harshness; rather it needs the following:
1. Kindness and gentleness
There are a number of hadiths in which the Prophet (blessings and peace of Allah be upon him) teaches us to use kindness and gentleness when interacting with others, such as the following:
‘Aishah, the wife of the Prophet (blessings and peace of Allah be upon him) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Verily Allah loves kindness in all things.” Narrated by al-Bukhari, 6024.
Muslim (2592) narrated from Jarir that the Prophet (blessings and peace of Allah be upon him) said: “Whoever is deprived of kindness is deprived of goodness.”
‘Aishah, the wife of the Prophet (blessings and peace of Allah be upon him) said, narrating from the Prophet (blessings and peace of Allah be upon him): “There is no kindness in a thing but it adorns it, and it is not taken away from a thing but it makes it defective.”
‘Aishah said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “When Allah wills good for the members of a household, He instils kindness in them.” Narrated by Imam Ahmad in his Musnad, 40/488, no. 24427; classed as sahih by al-Albani in Sahih al-Jami‘ as-Saghir, no. 303
Children by their nature love the parent who is kind to them and helps them, and who cares about them, but that should be done without yelling and getting angry, as much as possible; rather it should be with wisdom and patience.
The child is at an age where he needs leisure and plays; he is also at an age where discipline and teaching are appropriate. Hence everything must be given due attention, within moderation.
Because children love kind parents, this love gives them a strong motivation to obey their parents. In the opposite scenario, if kindness is absent and there is violence and harshness, that will lead to alienation, which in turn will lead to stubbornness and disobedience, or the prevalence of fear which will generate an attitude of lying and deceitfulness in the child.
2. Kind treatment does not rule out the use of punishment when necessary.
But it should be noted that punishment when bringing up children, must be used wisely. It is not right to punish the child for every misdemeanour on his part; rather punishment is to be used when kindness is of no benefit and when advice, instructions and bans have been to no avail.
Punishments should also be useful. For example, if you have the problem of your children spending a long time in front of the television, then you can dictate to them which programs they may watch, that will usually be beneficial and not harmful, and that are free of problematic material as much as possible. Then if they go beyond the stated time, you can punish them by depriving them of TV for an entire day. If they go beyond the stated time again, then you can deprive them of it for a longer period, according to whatever will achieve the aim and be of benefit in disciplining them.
3. Setting a good example
The parents must, first of all, adhere to the attitude and behaviour that they are trying to instil in their children. For example, it is not appropriate for a father to forbid his child to smoke when he himself smokes.
Hence one of the early generations said to his children’s teacher: “Let the first thing you do in setting my children straight be mending your own ways, for their faults will be connected to your faults; in their eyes, what is good will be what you do and what is bad will be what you refrain from.” (Tarikh Dimashq, 38/271-272)
4. A good environment
This is the environment in which doing good deeds is praised and the one who does them is respected, whereas bad deeds and those who do them are criticized. In current times this good environment is often lacking, but we can try hard, physically, psychologically and financially, to create it, in sha Allah.
For example, if a Muslim family is living in a neighbourhood where there are no other Muslim families, this family should try hard to move to a neighbourhood or city where there are a lot of Muslims, or to a neighbourhood where there are mosques or Islamic centres that are active in running programs for Muslim children.
For example, if a child is interested in a specific sport or other activity, the family could look for a suitable sports club or similar organisation run by committed Muslims, that is attended by Muslim families who are keen to give their children a good upbringing. Mixing plays a major role, as you say, so try to reduce the negative effects that you are seeing as a result of mixing, by mixing in a positive way with Muslim families.
If the father is spending on nice clothes, delicious food and a comfortable home, he should also spend on means of acquiring good attitude and behaviour, and let him seek reward for that with Allah, may He be exalted.