I have two little ones so will need to think about phones at some point in the future, for me the problem isn't smartphones its the internet as a whole, giving a child a smartphone gives them complete access to the internet and everything that comes with it.
If they designed a smartphone that could be managed by a parent, similar to who Amazon Fire Kids tablets are managed then I think it would be the best of both worlds - A feature phone is a safe option but there are features they don't have that I would like to leverage