Young kids need phones to be able to keep in touch with other family members or fiends. Phones would also give a way to contact there parents in a emergency. In my opinion most young kids need phones most kids get discriminated for not being "cool" for not having a phone of their own.
I don't think they need fancy iPhones like the ones shown in the picture. If parents are going to give their kids phones at a young age, it would probably be because the parents go on business trips a lot or the kids have medical issues. The parents would need a way to contact or reach their kids when in case of emergency. If their kids do have phones, they should probably give them flip phones or basic phones. That way both the kids and the parents have a way to contact each other. Not all young kids need cell phones, but in some cases it would be reasonable for them to.
I'm not exactly sure how you're defining "young kids" but I'm 14 and I don't have a phone and I'm doing fine. Most little kids aren't going to be in a situation where they need a cell phone. If they do need to call someone, there will probably be a landline nearby.