How do you understand “These became part of the child”?

(A lot of common objects have been enumerated in the previous lines, and here are the last two lines of the poem.) “The horizon’s edge, the flying sea-crow, the fragrance of salt marsh and shore mud. These became part of that child who went forth every day, and who now goes, and will always go forth every day. ” 
How do you understand “These became part of the child”?
【正确答案】：

THE COMMON OBJECTS IN THE POEM REFLECT THE NATURAL PROCESS OF A BOY’S GROWTH.

【题目解析】：这首诗中常见的物体反映了一个男孩成长的自然过程。