2 suggestions...within 1/8 block of one another, both perfect for your sis and nephew, and both so casual that they don't feel the need to have a website (GRR):
Nicky's Firehouse (pizza/Italian food)
David's Rumba Cafe (search for it on this board for details) for Latin food; everything from burritos to plantains to firecracker calamari
6 Elmer St
Parking is available on the street or in the muni lot right behind Firehouse, and when you park in that lot, Rumba Cafe is across Elmer St.