childish

2. Childish, infantile, childlike refer to characteristics or qualities of childhood. The ending -ish often has unfavorable connotations; childish therefore refers to characteristics that are undesirable and unpleasant: childish selfishness, outbursts of temper. Infantile, originally a general word, now often carries an even stronger idea of disapproval or scorn than does childish : infantile reasoning, behavior. The ending -like has pleasing or neutral connotations; childlike therefore refers to the characteristics that are desirable and admirable: childlike innocence, trust.

Example sentences from the Web for childish

We are not "equal" and you are not an ally if this is the childish base of your notions.
The Unbearable Whiteness of Protesting|Rawiya Kameir, Judnick Mayard|December 10, 2014|DAILY BEAST
The slimy, childish, petulant Viserys starts off as a symbol of everything about Targaryen rule Westeros has rejected.
Who Died and Made You Khaleesi? Privilege, White Saviors, and the Elusive Male Feminist Who Doesn’t Suck|Arthur Chu|June 24, 2014|DAILY BEAST
Why turn a genuine good-news story into an expression of childish pettiness?
What Is William and Harry's Problem With The Press?|Tom Sykes|February 14, 2014|DAILY BEAST
The gorgeous sushi chef he meets and falls in love with, Mi-do (Kang Hye-jung), is equally silly and childish.
What Asian Film Remakes Like ‘Oldboy’ Get Wrong|Jimmy So|November 26, 2013|DAILY BEAST

According to the blog, she soon “backtracked” on her comments, deleting the Facebook thread, and calling the brouhaha “childish.”
An Absurd Push for Separation of Religion and State in Canada|Mira Sucharov|November 15, 2013|DAILY BEAST
The most absurd faces, with sprigs of flowers stuck in the oddest fashion in their comical and childish heads!
Madame Chrysantheme|Pierre Loti
At times I felt as it were abashed, and even resentful of the various privileges of my childish years.
White Nights and Other Stories|Fyodor Dostoevsky
For Berlioz he kept the excited enthusiasm of a child, childish memory doing the trick.
The Life of Francis Thompson|Everard Meynell
Had she shown "my puppy" her childish qualities, he would have despised her—he had left that department himself so recently.
Hard Cash|Charles Reade
The winning expression of innocence and gentleness in her mild, childish eyes particularly struck him.
The Catholic World, Vol. X, October 1869|Various

British Dictionary definitions for childish

childish

/ (ˈtʃaɪldɪʃ) /

adjective

in the manner of, belonging to, or suitable to a child

foolish or petty; puerilechildish fears

Derived forms of childish

childishly, adverbchildishness, noun

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012