I'm sure every monarch and their consort are "attentive" to their children as possible, but it's undoubtedly true that when a couple reach the top job they simply cannot be as present in their children's day to day lives as possible. From Charles in our own according to kornet, "3rd world" country, to Frederik in Denmark and Victoria in Sweden, they all have stated that they saw less of their parents than they would've liked to when they were growing up.
As regards Charles, I don't see why you see a short reign as any type of disappointment. History has shown that short reigns can be very effective and also very popular. Edward VII reigned very successfully for less than a decade, as did George VI for 16 years. Charles could conceivably reign for 20+ years.
If Charles had been King for the last 20 years, the UK would be very much the poorer. The constraints of the top job would've meant his charitable efforts would have had to be put aside, and William would not have been old enough or experienced enough to take it on.
More generally, I just don't understand this idea that monarchs can 'resign'. It just feels wrong to me. Will Princess Beatrix have to curtsey to her son and daughter-in-law now?