Acting like a five year old is to metaphorically throw your arms in the air and flail them around, all the while screaming or pouting (you choose) and doing a little stomp dance with your feet. It is an attempt to get your own way, in your own time, and at your own leisure.
It is the epitome of selfishness and pride, thinking you are the only one that matters.
Acting like a five year old as a daughter of God is to then be gently and firmly chided for your actions and coming to the Lord with tears of remorse and sorrow knowing that what you did was wrong. It is finding comfort in His arms and asking His forgiveness.
It is receiving from Him the gifts that He seeks to pour out on us even in those times that we know (without a shadow of a doubt) that we don’t deserve them.
It is the epitome of love and grace, knowing that you are the only one that matters to Him.
What a beautiful God we serve.