Middle Child, the always-busy Center City diner, is getting a new sibling.

A big new sibling.

Matthew Cahn confirms that he’s opening Middle Child Clubhouse — more than five times the size of the original location and including a bar — this summer at 1232 N. Front St. in Fishtown, under the El and across from Front Street Cafe.

Thematically, “it’s really not much different,” Cahn told me, comparing the three-year-old original on 11th Street near Locust, which puts a quirky, modern spin on the classic luncheonette experience. “We’re just putting our big boy pants on. We always talk about never growing up. I think that we can put some nice slacks on every once in awhile.”

Both Middle Childs will be the same by day, serving breakfast and lunch (eggs, overstuffed sandwiches, salads, etc.). At dinner time, Middle Child Clubhouse will have a full menu, real place settings, and a bar. “This is Middle Child-plus-plus,” Cahn said.

At 100 seats, compared with 16 on 11th Street, “it’s not going to be a sardine box. There will be more room to hang out.” He’ll offer WiFi and coffee.

He’s not revealing other details just yet but says there will be a pool table and disco ball, as well as “curve balls” when it comes to programming.

Among the possible features are a beer garden and jungle gym. “I’d love for half of the restaurant to be a Dunkin’ Donuts,” he said.