Kids.. 😕

I feel so incredibly bad for my SO.. he loves his children very much but they don't show the same kindness they should. They didn't care it was his birthday, they didn't say anything to him despite him saying it's his bday over and over.. but when his oldest had his bday recently he was so happy to recieve gifts but didn't say thank you. They have zero manners, they never say please they never say thank you. They actually expect things, the oldest came up to me just before bed and said, "I'm going to just have one candy." I said no you're not. If you try and talk to them on occasion they will look at you and ignore what you say, won't even say anything just ignore you on purpose especially if you tell them to do something. Frankly they are selfish, and we can't fix it. I understand if they were much younger but they are 10 and 6 almost 7. Makes me want to take them to a place to see how people are struggling, to learn to have respect and compassion but more so to be THANKFUL. We don't have them full time so what progress they make seems to not stick with them when they come back. They tore the light out of the ceiling in their bedroom, not only could that of electrocuted them but they could of started a fire. They didn't say sorry, they didn't feel bad. They just don't care. I don't understand why? Any advice at all? It would be much appreciated.