It's completely different when you have your own kids though because you have them from day dot and can instill the types of values and behaviour in them that you think is acceptable. My kids will do the 'I want what they have' thing too, but you nip it in the bud and tell them no, they can't have it just because their brother/sister has it. It sounds like the 4yo is pretty high maintenance, so Mum has just gotten into the habit of indulging the 4yo to keep the peace instead of trying to teach them that they don't need the same amount of presents and don't need to get a present just because it's the other child's birthday etc. I promise it wont be like that with your own kids at all.