There is a saying in hindi
Bacche bhagwan ka roop hote hai
Kids are incarnation or manifestation of Bramhan.
Since Bhagwan is used to refer Bramahan or the Ishta devta (for Smartha people). So this means that it is just a saying derived from the happy and blissful nature of kids(since bramhan is Sat-chit-Ananda) or it has a scriptural basis?.