Your late husband was a legend! Sometimes a spade just needs to be called a shovel.
I was out with a friend in a pub the other day and there was a piano. The piano lid was down and had a sign on saying "Our piano is only to be played by pre-booked performers. Kindly do not allow children to play on the piano". This dad came with his two kids, probably around age 3 and 5, MOVED THE SIGN, lifted the lid and let the kids bash on it. They made a horrible racket. We told one of the floor staff, and she looked scared and said "oh, well normally we'd say something but they're with that big party over there". I said if you're not prepared to stop them ruining our meal because they're putting more money behind the bar than we are, you can afford to give us our dinner for free then. Lo and behold, she went and got the manager. Dad then spends 10 mins trying to gently persuade the kids to come away from the piano, eventually resulting in an epic tantrum by the younger child while he stood helpless and the older one continued bashing the keys.
Eventually my friend, who is a foster parent and has dealt with many a difficult child, went over, lifted his hands off the keys, shut the lid, gently but firmly guided him towards his father, told dad to pick up the younger one and get them back to their own table, as we thought we'd come to a pub, not a zoo. My friend has that way about her you don't mess with, and sure enough, he somehow scraped the tantrumming kid off the floor and disappeared with them.
Some parents need to learn how to explain to their children that sometimes in life, you want to play on the piano and you're not allowed to, and you have to respect the no even if it makes you sad, and even if you think it's not fair.