As a FA, I observed many military wives traveling with 2, 3 or even 4 children to/from Frankfort, Germany and the US. It is HARD, but doable. When you need to use the lav, press the call button and a FA will sit by your children while you use the lav. They usually will not hold the children, but they will keep them from harm for the two minutes you are gone.
The mother should eat a full meal before boarding and skip the meal service. Pack many mini baggies of finger food for the children. Also bring a plastic bag for your trash (this will help keep your area from being littered in half eaten goldfish and gummie bears). Consult your pediatrician about the use of a mild sedative (like benadryl) for the children, especially on a night flight.

For boarding, ask for preboarding. Beg if neccessary. If that isn't possible, board last. On arrival, let everyone else disembark first.

Good luck!