assuming you meant "humanely", which would narrow the category considerably, my suggestion would be Diner (on Broadway and Berry, in Williamsburg), which sources all of its steak from Marlow & Daughter's butcher store, which sources all of its meat from local, sustainable farms and has primarily pastured meats (ie, grass-fed, not corn-fed). Before going, give the restaurant a call to see what steak is on the menu that night - it ranges from a rib-eye for 2 to a 6 oz bistro steak. It is a very kid-friendly place, to boot.
Marlow & Daughters
95 Broadway, Brooklyn, NY 11211