I never heard of married kids “demanding” a down payment from their parents. If they are demanding, than they were obviously brought up in a way that their parents spoiled them and always gave them what they “demanded”. Otherwise they’d never have the gall to ask.
My siblings in Lakewood payed for their own down payments. And the ones that didnt have enough to put down took out a loan and are slowly paying it back by living with less. I would never ever ask my parents to pay for my down payment, let alone demand that they do. I was brought up not to “expect” things coming to me