English is a funny language, isn't it? We have all kinds of words that sound the same, or sometimes are even spelled the same, but can still mean different things. This causes lots of clever people, like computer developers and inquisitive 6 year-olds, all kinds of problems. One classic example is the observation, "Time flies like an arrow; fruit flies like a banana."
You'll have to tailor this somewhat based on your little boy's familiarity with Scripture, but, in much the same way as this somewhat silly phrase, the word "like" in your young friend's question has two different (though similar) meanings. We are commanded to be Christ-like in our behavior, speech, and attitudes. It is (among other things) by loving our fellow believers [like] Christ has loved us that we are to distinguish ourselves from other religions and sects. This speaks of our character and redeemed priorities.
Satan, on the other hand, tempted Adam and Eve to be like (i.e. equal to) God in Knowledge (explicitly) and Authority (implicitly). Trying to be "like" God in this sense is everywhere condemned in Scripture since it is an attempt to upend the order of the universe itself; dethroning God and replacing Him with ourselves. Clearly, this cannot be what the apostles and other New Testament writers had in mind when they write about the necessity of being Christ-like. It is also antithetical to the submissive and humble nature which Jesus displayed in consenting to leave the glories of Heaven (to which He had every right) and come to earth at the request of His Father; born of a virgin into a poor family, so that He could die a painful death for our woefully ungrateful selves.