Why is it not appropriate to use an adult EQ-5D-5L value set to derive EQ-5D values for the EQ-5D-Y-5L?

At present, value sets for the EQ-5D-Y-5L are not available. The use of adult EQ-5D-5L value sets to generate EQ-5D values for EQ-5D-Y-5L health states is not recommended. The EQ-5D-5L and EQ-5D-Y-5L descriptive systems differ somewhat and preferences for child health may differ from preferences for adult health, which means that a value set for the EQ-5D-5L may misrepresent values for the EQ-5D-Y-5L. For those reasons, we do not recommend using an EQ-5D-5L value set to derive preference weights (utilities) for EQ-5D-Y-5L health states.