We must come to Christ "like a child".

A heart that repents--WE MUST ACKNOWLEDGE SIN. To enter into the Kingdom of Heaven we must first have a heart willing to see the sin in our lives.  People are willing to say that they have sin, but then they want to create their own god who will lovingly overlook that sin and place allow them into heaven.
Turning from your sin means that we see our sin as disobedience against all mighty God, so we strike that sin from our lives.  How do we do that?  Jesus gave an illustration :

“If your hand or your foot causes you to stumble, cut it off and throw it from you; it is better for you to enter life crippled or lame, than to have two hands or two feet and be cast into the eternal fire.

A heart that is humble--Jesus used the illustration as a child to bring out the point of humility.  Notice how the child that Jesus summons to himself, immediately comes to Jesus.  That is humility- no resistance, total trust.

The most powerless members of ancient society were little children; in most of ancient society, age increased one’s social status and authority. In Jewish culture, children were loved, not despised; but the point is that they had no status apart from that love, and no power or privileges apart from what they received as total dependents on their parents.