Scriptures encourage us to be childlike but never to be childish!
Being childlike is inculcating the good virtues of children in your spiritual development.It makes you to have a teachable and receptive spirit throughout your life.
“I tell you the truth, anyone who doesn’t receive the Kingdom of God like a child will never enter it.”-Mark 10:15
What about childishness?
To be childish is to be immature.It is wallowing in the low grade emotions like anger,quarrel,envy, jealousy etc when you are supposed to be well above them.It is feeding on milk instead of solid food and being satisfied with it.
Apostle Paul has good responses for this:
“But for right now, friends, I’m completely frustrated by your unspiritual dealings with each other and with God. You’re acting like infants in relation to Christ, capable of nothing much more than nursing at the breast. Well, then, I’ll nurse you since you don’t seem capable of anything more. As long as you grab for what makes you feel good or makes you look important, are you really much different than a babe at the breast, content only when everything’s going your way? When one of you says, “I’m on Paul’s side,” and another says, “I’m for Apollos,” aren’t you being totally childish?”-1 Cor 3:1-4
“When I was a child, I spoke and thought and reasoned as a child. But when I grew up, I put away childish things.”-1 Cor 13:11