Although e.e. cummings has quite a bit of "non-serious" poems out there, he can also has many, many poems that are perfectly serious, grave, and deeply profound. If you have a chance, peruse some of this other poems, and you will discover the range and variety of his poetry--from silly to serious. To give you one example of a very serious one, look at his poem "somewhere i have never traveled"; I provided a link below. As you read through that poem, it is apparent that it is very serious, and that his love for this woman is something that he considers to be deeply profound and layered. One would be hard-pressed to call that, and many other of this poems, silly or light-hearted.
However, often his poems are quite light-hearted, silly, and exist merely as a way to experiment with language and rhythm. Some of them come off as almost like nursery rhymes in their ridiculous and jocular subjects and structure. One example of this is "anyone lived in a pretty how town." It is bouncy, rhythmic, and seems to be very childlike in its jabber-talking. However, the apparent silly surface and structure of the poem masks a deeper, morose message of a man's life that was so insignificant that he didn't even have a name worth remembering, that no one really cares about when he dies. The poem is about how people just go about their days, caring very little for others, and forgetting those that have gone before them. His usage of the "non-serious" style of writing emphasizes the childlike, flippant way that we go about our lives, and underscores the importance of a man's life, just like everyone around him did. It takes a serious subject of one's impact in life, and makes it trivial and unimportant, just like we often do ourselves. It is a symbol for our attitude towards others, and cummings, being a poetic genius, reflects our glib attitude in his glib style of writing.
I hope that those thoughts help get you started thinking about the poem a bit; good luck!