Yes. The median household income in the US is $68k. Even at the poverty line for a family of 4 at 26k[0], $1600 in phones for your two children that last 2 years+ is worth it given the immense value it provides, both in time savings (spending hours a day texting / via entertainment) and utility.
Almost every kid I know gets their parent’s old phones. Apple made a major effort to extend the supported usable life of their phones several years ago and it’s paid big dividends in terms of getting the kids started on iOS. A brand new $400 SE can easily be expected to give 5-7 years of service, which brings the starting price down to $60-80/a to say nothing of the used market. It’s hard to even argue that Android is the cheaper option unless you don’t mind running insecure OS versions for several years.
Is this because US people have a lot of disposable income?
Just iPhones are pricy even secondhand. Of course Android doesn't update for as long but plenty of people worldwide run unpatched devices.