Chinatown for a large group
A big dim sum palace (eg Jing Fong on Elizabeth) has no problem absorbing 11 people. Slightly more upscale, Ping's (on Mott) also takes large groups and consistently gets high ratings. They have both a smaller veresion of dim sum ( eg minced shrimp in dumpling wrapped in crisp bacon) and a regular menu at lunch (including diced squab with veggies in a crepe). They might be a little more expensive than Cafe 4-5-6.
You have lots of options - even some Sichuan.
I often have large parties at Congee Village on Allen St., the latest last week. They have several private rooms, the food is mostly delicious (especially the garlic chicken and the seafood ) and a full bar (most rare in Chinatown). They also take reservations on the phone, even in English! I heartily recommend them. And there are always tons of children.
Count on about $35 a head for lots of food and relatively heavy drinkers, less is less is drunk. they do have good lichen Martini's.
I want to thank you all for your suggestions. We did end up at Cafe 456 on Mott Street, and it was perfect for the mixed group that we had. We were a party of 11 and the waiter was good at recommending dishes and making sure that there was enough food and drink. He was patient in showing everyone how to eat the soup dumplings, and had a sardonic sense of humor which cut through the language barrier. We arrived early for our reservation and the table was ready for us. The place was packed on Saturday, with a line on the street, but we were not rushed at all.
Highlights of the meal for me were the cold sesame noodles, crispy duck, and string beans, eggplant and broccoli in spicy basil sauce. I do not eat pork, so did not have soup dumplings, but they received raves. I also liked the veg. dumplings as well.
There was nothing ethereal here, but the food was solid, the atmosphere was pleasant, and the service was very good. Recommended.