The kingdom of God belongs to the childlike. What Jesus really means to say is that we need to become like babies, infants, those helpless defenseless non-speaking little humans who look around and behold the world with eyes wide open.
And when our eyes are wide open without defenses we will return to Eden: all at peace with one another, even the wild animal within us.
The Peaceable Kingdom, c. 1834 (Edward Hicks, public domain)
The Biblical vision (Isaiah 11)