You’re very lucky. My father met my oldest son when he was just learning to walk. Then he had a heart event (don’t know if it was a stroke or a heart attack) that blew out his short-term memory. Unfortunately, you need short-term memory to facilitate loading into long-term memory. So, my next two sons were born after the event. When we repatriated, my father could never remember the younger sons’ names, but could the oldest’s name. They used to walk with him when they could, but he had lost a lot of his speaking abilities, too. You and your kids should cherish the time they have with their elders.