Since vs when

When western children have a gap in their lives, such as the lack of a father, their imagination fills that gap. A fatherless child, for instance, will invent an imaginary father ----- he sees other children's fathers. They are far more interested in material possessions that in friends. He doesn't directly cut the need of a father or mother. His feelings will help him to fill in that gap.

1) since
2) when

Although grammatical, #1 seems a bit out of place to me. I believe #2 is the best option, meaning "whenever, each time, as soon as or at the point in time when it happens". What do you think?