Presented as an episodic bildungsroman, We the Animals truly does reverberate the theme of discovery. Why is it episodic? It is episodic because it is presented in different "episodes" which don't necessarily need to be read in the order presented (and yet each "episode" has that same theme of discovery). The theme of discovery itself lends to the determination that this is truly a bildungsroman. What is a bildungsroman? Quite simply, a bildungsroman is a coming of age story. Those things being said, now let's look at the theme of discovery which you would like to learn more about. In fact, let's take the five different episodes separately.
In "We Wanted More," the theme of discovery is best shown in the boys/wolves slowly gaining the knowledge that their "alpha-male" father wants to teach them something. Specifically, he want to teach them of an element "beyond the pain." We can take the theme of discovery to a deeper level by noting the boys/wolves also "discover" that their father is the authoritarian and that their mother (being languid and "done") is certainly not.
In "Never-Never Time," as an obvious reference to Peter Pan, the theme of discovery is best shown not in the obvious vegetable mess the boys create, but in their discovery of their mom as a needy and sad creature. The boys live while their mother sleeps (during off-time at the brewery). They have fun smashing fruits and talking with mom as she wakes up, confused. The boys relate how this reminds them of their birth. Mom wants to be a part of it and asks to be made "born." They boys are shocked into reality here: the truth that their mother is a sad individual.
In "Heritage" the theme of discovery is best shown when the boys realize they cannot please their father by being themselves. The father (even though he is drunk) wants his boys to dance to his favorite music. The boys "wiggle" and squirm, but are unable to dance as their alpha-male father wants them to. The theme of discovery can be taken further when we realize, as readers, that the only way the father was able to achieve the "dancing" he requires of his boys is by being beaten in his own youth.
In the episode called "Seven," the theme of discovery is best revealed in the boys' desire to protect their tired and beaten mother. They are "growing up" by feeling that protection. They prove themselves to be better than their own father in that particular way. However, if we take the theme further, we see that the nature vs. nurture idea is "won" by nature when each seven year old child now refuses the tenderness of mom. Further, when they turn seven, they tend to take on the brutality of their dad.
Finally, in "The Lake," the theme of discovery can be determined by what is the best way to learn as opposed to the father's "only way to learn." The father, in his prowess, takes the mother and son out into the middle of the lake where they are not able to touch bottom. Likewise, they are not able to swim. Unfortunately, leaves stick to them and the father throws them. The mother panics and clings to the son, scratching him in her terror. No one dies, but everyone is rattled. The father insists that this was the "only way to learn." Taking the discovery theme further, the reader should note that the boy discovers that, by swimming on his own (no matter how crudely), he can be his own person and free from the control of both father and mother.