I believe you will get many answers and opinions in this matter.
Here is one such opinion :)
Kids are the new generation. Their minds are pliable and they listen to what parents and elders tell them (mostly). That does not mean one can put upon the child all the beliefs that One thinks is right. For instance, does the parent know for sure that one must pray to God? Does the parent know who God is? Does the parent know why one must pray? Then how can the parent/elder force upon the child these beliefs which he/she himself/herself is unsure of. This is the age to explore, to seek, to find, to follow. The duty of elders is to create the right platform for the children to explore.
For example, think of a game. One likes one sport but someone else likes another. This is because when it comes to sports, parents give the right platform for their children to explore, to play different sports, to play what they like (without abusing others/themselves). That helps the children to grow into lovable beings. Sportsman spirit is developed. However when it comes to religion, parents always use words such as 'you SHOULD pray' 'God will PUNISH if you don't' etc. (Please note that this is in no way targetted towards the OP or any other specific parent).
There are many many paths to God. One of them (some say it is the best of all paths even!!) is Bhakti or doing prayer. Even in Bhakti there are various ways to do it. Pooja, Japa, Dhyana, Smarana, Vandana, Pada namaskar, Kirtan, Sharvana, Reading, Seva, etc. So the duty of the parent is to say "Prayer is good, there are many ways to pray. You yourself pray and find out for yourself whether or not your quality of life changes, I will provide the right platform to do so." Provide right platform for child to seek and find out what prayer is and how it transforms the child, without abusing others/himself. :) Ensure that good values are being cultivated, like forbearance for others, patience, love for fellow man (and woman), respect for animals, service to humanity, right attitude towards knowledge (knowledge is continuous and evolving, but being knowledgible does not make one superior to others!), finally respect for all religions and ways of life. (in a childish note, God will be happier if His children are good but do not praise Him, rather than if they praise Him and cut the throat of another.)
Secondly lead by example. Seek for yourself, Who GOD is. What prayer is? Why should one pray. When you truly pray and seek God with your Heart, you will yourself be transformed isn't it? On seeing your efforts and seeing the transformation that occurs in YOU as a result of your prayers, the child will be naturally transformed :) All the best sir.