As an adult, I have never had a landline in my home. I now have several pre-teen kids and none have their own cellphone. When the older ones are home alone, I leave out an old iPhone that is connected to the home wifi network; that's enough for them to call family (through Facetime) or 911. But this isn't ideal because the phone is not always charged or the younger kids hide it. Is a landline the only real solution?
Land line is the safest bet.
In the US at least, there's also a guarantee that there will always be a dialtone on a paid line even if you have a power outage in your home (assuming of course that you have an actual traditional un-powered phone plugged into the line).