Actually, Apple phones remains serviceable (Apple stocks parts and will repair) until they are 7 years old (obsolete , in Apple speak) or older in places where law requires that.

At five years (vintage), operating system updates usually stop - and by then, cell phone technology sometimes becomes obsolete - for example, 3g is now almost gone and the 5S and older will not be able to work when your carrier kills it: https://www.phonearena.com/news/when-will-verizon-t-mobile-att-phase-out-3G_id125233

You will not necessarily save money by switching away from Apple. Cheap smart phones are not well made and will not last long. The cheaper ones do not usually keep operating systems up to date, exposing you to security risks. The well made phones that are kept safe cost as much as Apple.

BTW, I assume you know about protecting your daughter with the built in Parental Controls: https://support.apple.com/en-us/HT201304