I cannot believe some of the comments regarding children on this thread, I can only imagine that the posters either know nothing about children or simply don't have them.
People with young children must be seated together, as F3G points out for safety reasons than any other. It is simply not practical to seat a 3 year old child 10 rows from their parent. Of course the reason RYR have done this is because they know that most parents will not risk being separated from their children. Let's add this up, what percentage of passengers are either children or those travelling with children ? Say 30% ? 30% of 40 million passengers is 12 million. At 2 pounds per person this adds up to £24 million per year.
Another reason why I'll never fly with RYR again.