Bishop Richard Allen parallels Mass Ave and goes one-way the way you need for your return trip. At its end near Inman Sq, you can take a little jog around to hook back up to Harvard St which is two way by then.

You might PM Ya Ta Sabes on here. He lives in Somerville between Inman and Union and has a rugrat of his own, though I don't know if he hauls him around or not.