There is an issue in the starter for tabs. It does not have a ion-nav element: https://github.com/driftyco/ionic2/issues/877
https://github.com/driftyco/ionic2-starter-tabs
It was fixed for the js version, however it looks like you are using the typescript version (which you can find under branches). However the Pull Request was not accepted yet.
Essentailly you want to make another page for the tabs pull out the html thats in app.html into there and make a controller that imports your pages.
Then in app.html add and in app.ts import the TabPage and set it as root.