Dhikr is very highly emphasised this month. Why not gift them a tasbeeh if they don’t have one already, and keep it near their bed as a reminder to do dhikr just before they go to sleep.
In particular:
1. Asking for forgiveness – The older ones can recite Astaghfirullaha wa as-aluhu tawba. (I seek forgiveness from Allah, and I pray He accepts my repentance.) whereas little ones can simply be encouraged to say i’m sorry for every bead, and think about something they may have done wrong.
2. Repeating Laa ilaha illAllah (There is no God but Allah). Share this awesome hadith with them! The Holy Prophet said that if we recite it 1000 times, Allah will grant us 1000 rewards and houses in heaven. Ask them to imagine this as they are reciting!
3. For older children, the following dhikr can be done: The Prophet said that we should recite Astaghfirullahal-ladhee laa ilaaha illaa Huw, wahdahu laa shareeka lah, wa atoobu ilayh (I ask forgiveness from Allah Whom there is no God besides He, and He has no partner, and I repent before Him) 400 times. The reward of that will be the same as 100 martyrs would receive!
And let’s not forget to do these dhikrs ourselves Inshallah!