Not at the age of 3-6 years please, let children enjoy their childhood. Yes a child’s brain picks things faster at an early age but please don’t put pressure as a child’s brain isn’t that developed to grasp things that are difficult to understand at a young age. Children are too young to understand prayers and even hymns but you can start sadhana by the age of 7-8 years. Off course let them play but slowly you can start teaching them classical singing, classical dancing and recitation of hymns like Ramraksha stotra, Ganpati Atharvashirsha, Hanuman Chalisa, Bhimrupi and much more.
It helps them get acquainted with GOD and makes them naturally GOD fearing. Recitation on a daily basis instills discipline in their spiritual ascension journey. Say you start at their age of 8, your child by the age of 18-21 years will be ready to face the outer world – imagine the credit they accumulate in their spiritual bank account by way of sadhana. GOD uses this sadhana to clear out many obstacles they would have had to face otherwise due to past life or ancestral karmas in their bloodline. When do you and me start building our credit? After retirement because we feel it’s a retirement job. No start early but do it out of love for GOD.