Purity is an attribute which humans strive for but can never achieve on our own. Only God is absolutely pure, we are born sinners and so it is only through the sacrifice of Christ and subsequent work of the Holy Spirit in us that we can be purified.
I start with this to emphasize that in praying for my kids to be pure, to have pure hearts and clean hands, they must be in Christ. Purity is impossible apart from the work of Christ and even for those of us who are born again, purity only comes through the work of God in us, not merely by our own efforts.
When I consider my son, who is currently two and a half, I can see an innocence and purity of motive within him. Yet there is also deviousness, selfishness and sin in there too. Small children are about as pure-hearted as humans get so we want to keep them that way as long as possible. However, sin is relentless in our hearts and will have its way when left unchecked.
So I am praying for faith to be given to my children, that they may know Christ and His purity from a young age. I want them to be transformed by the washing of God’s words, by the whisper of His Holy Spirit to their conscience and by the growing fruit of righteousness in their lives.
He who has clean hands and a pure heart,
who does not lift up his soul to what is false
and does not swear deceitfully.
He will receive blessing from the LORD
and righteousness from the God of his salvation.
(Psalm 24:4-5 ESV)