I my opinion it is a bad practice, Railway have to provide full berth to children who had purchased half ticket. Only one thing railway can do is that if there are two children then both can be allotted 1 single berth as they can adjust easily on same berth but children aged above eight years is difficult to adjust with their adult companion.
If railway want to increase it revenue then withdraw all concessions including Sr.Citizen and any other relaxation provided in 2AC, 1AC, Rajdhani and Shatabdi.