I recently just set this up for my 5 year old.
I bought a Grandstream HandyTone 801 as a bridge. I use voip.ms as a service provider. Both are geared toward more technical users, but the service is very reasonable for the price. Instructions for configuring it are clunky but not too bad: https://wiki.voip.ms/article/Grandstream_HandyTone_802_-_HT8....
I had previously tried Ooma, but I didn't like that it wanted to sit between my router and modem.