I saw that some people were mentioning how the imaginary friends resembled a certain aspect of each of the children's personality or someone they knew. I feel like there was something in Hollow that people might not notice.

Hollow: While Hollow looks like an angel, you'll also notice that she has a winder on her back. In the game, Boris (A.K.A. The Ghost) referred to Anthony as a toy. So, Hollow does resemble a wind-up doll. It does make me think that Anthony's parents were never nice people. The moment Anthony was suffering from depression and schizophrenia (some of the symptoms are a little similar), they got cruel with him. Then, send him away so they don't have to deal with him anymore. Similar with a broken toy. The absence of eyes could represent Anthony's trust issues. The inability to see the reality of his parents or grown-ups in general.