Infantly, a word that implies acting or behaving like an infant, has a variety of synonyms that can be used depending on the context and tone of the sentence. Some alternative words to infantly include childishly, naively, immaturely, foolishly, unintelligently, and babyishly. These synonyms can be used interchangeably to describe someone who is acting in a way that is not appropriate for their age or level of experience. It's important to choose the right synonym to accurately convey the intended meaning and context of the sentence. Ensure that the chosen word matches the tone and context of the sentence for effective communication.