Internalizing disorders are a public health issue affecting up to 20% of school-age children, yet few receive assistance. Internalizing difficulties can emerge in the preschool years, with stability from this time onward. To inform prevention programs, knowledge is needed about early internalizing indicators in community samples. This study describes initial development of the Children's Moods, Fears, and Worries Questionnaire, a parent report measure for toddler and preschool internalizing difficulties. Potential internalizing indicators were identified via literature review and pilot testing. These indicators were empirically examined with 112 parents of 2-year-old children drawn from the community and followed longitudinally to age 4. Parents rated their child on symptoms of anxiety, depression, inhibition, peer withdrawal, and separation insecurity. The new questionnaire included items that grouped statistically at 2 and 4 years. It demonstrated internal consistency, test-retest stability, and initial construct validity. While further research is needed to assess predictive validity and to establish clinical cut-points and community norms, the questionnaire appears to be a useful instrument for assessment of young children's internalizing difficulties.