Jacob's children are practically nonexistent, and maybe that's the point. They have abandoned him at a retirement home and moved on with their own lives. He can barely tell them apart anymore.
It's hard to tell if Jacob got sick of his kids, if they got sick of him, or if it was mutual. Perhaps his children got tired of taking care of him. Perhaps Jacob got tired of no longer being the most important person in their lives. It's possible that if Marlena had lived longer, the whole family could have stuck together. Maybe without her there, the family just drifted apart.
Whatever the reason, Jacob has become dramatically estranged from his family. It's almost like they don't know each other anymore. The crowning indignity is when one of Jacob's children, Simon, really does abandon him by forgetting to show up and take him to the circus. This forgetfulness, which seems needlessly cruel at first, turns out to be a good thing in the end. It's the push Jacob needs to get himself out of the old people's home and back into the world. He leaves the home and goes back to what he feels is his real family, the circus.