A child’s vocabulary ability may be influenced by many different factors in their home environment. The present study focused on supportive aspects in home environments and the relation to children’s vocabulary size through an online study where 166 parents of children aged 47.63 months (range 33.7–59.9 months) responded. Children’s home literacy environments were positively associated with children’s vocabulary size. Aspects of the home environment such as the parents engaging in teaching colors, and letters and talking about daily activities showed a positive association with vocabulary size. Print book reading was important, but the number of books the parents read did not seem to be associated with vocabulary size, rather whether the parent was engaging in dialogical reading and discussing the books, explaining the content, and relating the content to the life of the child mattered. Digital media (screen media and digital games) did not show a positive association with vocabulary, regardless of content or parents’ joint media engagement. Watching screen media showed a negative association with developing vocabulary. This association was, however, ameliorated when positive influences and activities in the home literacy environment were present.