We investigated the conceptualization of values as mental constructs at the beginning of middle childhood. Values describe aspirations guiding individuals in life. Although 6‐year‐olds report meaningful values, a past cross‐sectional study suggested they may conceptualize them in non‐mental terms. We interviewed children on their values at two time‐points (N = 299, M age T1 = 7.25 years, Mage T2 = 7.94 years). Mental value conceptualization increased over time. Different value types were conceptualized in mental terms to a similar extent. At T2, self‐important values were conceptualized in mental terms less than not‐important ones. We also suggest that Theory of Mind (ToM) may be an underlying mechanism for the increased level of mental conceptualization over time. A cross‐lagged panel model indicated that T1 ToM predicted advances in T2 mental conceptualization, and T1 mental conceptualization predicted advances in T2 ToM. As children develop in their understanding of the social world, their values may transform from observable to mental, possibly making them better motivators of behavior.