I'm fuming... It was my little boys 4th birthday today and I bought him a box of kinder eggs as…

I'm fuming... It was my little boys 4th birthday today and I bought him a box of kinder eggs as they're his favourite chocolate. They were in the kitchen and whilst my sister in law was here with my two nieces, they took the kinder eggs to my sons bedroom and ate the lot between them and left all the wrappers in his bed. My son looked devastated that they were all gone when I took him to bed. My son would never take something like that without permission so I'm so shocked to have something like that happen to him. I know they're not exactly expensive or anything massive but I'm so angry. They're 4 and 6 years old so should know better. I've not said anything to my sister in law because I don't want to cause an argument or accuse her girls of anything as they're obviously going to deny it but I'm so angry!! 😡😡