When I am flying on an international flight, with a 777, I always try and get the seats in the VERY last row. It has several advantages:
1. The other rows have three seats; this row has two. You can seat your child by the window, next to you, and with no one else in the row.
2. It is near the bathrooms, water, etc. And the service cart is almost never blocking your way.
3. There is about half a seat of extra space next to these two seats. This makes it easty for you to get up to stretch without bothering others.
The DISADVANTAGE is that you will be one of the last persons off the plane. Don't use if you have close connections.....