Indeed. Several years ago, when booking your own flight online was in its infancy for the masses, and the idea of choosing a seat online was barely heard of, I booked five tickets for me and my family. Two of the three children were under 11 and booked as such.
When we got the departure airport, we discovered that we were seated all over the plane, with no-one near each other. After much loud complaining, especially along the lines of 'my six year old daughter is sitting with a parent or we will shout even louder' it got sorted. But not a pleasant experience at the time and a lesson learnt.