You can't restrict callers as easily on a landline phone. You can block individual numbers, but most landline providers won't let you block by default. I can only imagine the support calls Comcast would get from people following some "never get spam!" guide but then not being able to get calls from their doctor or the plumber.

If you're handy with tech like most folks on this forum, you can do all this yourself through a voip provider for significantly less per month, but you don't get a nice app interface to configure and you'll have to scrounge and hack to get cute hardware for your kid.

This one is wifi based, made for kids, it has a free plan, safety and security features. Pretty well put together.