I don't know CX's official policy, but I would definitely complain as a F passenger. You didn't pay F tickets for them so they should not be allowed in F. As simple as that no matter what age they are.

If you want to see them, then go back to economy.

When we travel, we all fly together in F or J. Kids are now 4 1/2 and 1 1/2. Split cabins will happen when the kids are older and can take care of themselves.

P.S. My 4 year old was perfectly fine in SQ's F (77W) and CX's F (77W) by herself. I explained to her the seat arrangement before the flight. When she wanted to sleep, she would sometime come over and sleep with one of us.