Golf4food summed it up pretty well. But I'll post anyway, if only to see myself type.
Not knowing the ages or temperments of the children in your party, I'd say go with Biergarten. The show really is fun and its generally a more accepting environment for kids. Not that Le Cellier is not kid friendly, because it is, its just that Biergarten is more casual.
If you really want the steakhouse, and the kids are older and/or do well in sit-down restaurants, then Le Cellier will be fine as well. Its not the greatest steakhouse in the world (or WDW), but its solid.