I think rojon could probably do without hearing about other people's fabulous relationships with their children. Some of the contributions come across as rather smug.
There are lots of different sorts of parent/child relationships. Some parents have been so generous with their time, help and money that they are taken for granted by their children and those around them. I know a woman who looked after her elderly mum until her death, who cared for her unkind and unfaithful husband after he became wheelchair bound and up until his death several years later, and who has always helped her children in every way she can. She's now in her seventies and is still providing childcare for grandchildren. And yet her sons and daughters don't seem to reciprocate in any way - quite happily going abroad on holiday and never inviting her. Her children probably don't see themselves as uncaring, but they probably don't even realise that their mother is getting older and that she might need their support for a change (not that she ever complains). When somebody has always been so cheerfully capable and available, there is a risk that their contribution becomes so much "part of the scenery" that it's not even noticed.
Conversely, children who have had less supportive and caring parents may continue in adulthood to try and "win over" their parents by being overly attentive and sensitive to their feelings - sometimes to the detriment of other relationships.
rojon It must be upsetting to feel that your children are fairly near and yet they're unable to spare more time to come and visit you. I would feel the same. They are, no doubt, very busy with work and families, and, in these difficult times, it's easy to become preoccupied with one's own problems and assume that other people are managing OK. I don't know what the answer is except perhaps to let them know how much you enjoy their visits when you do see them.