There are currently many mathematics anxiety rating scales designed typically for adult and older children populations, yet there remains a lack of assessment tools for younger children (< 7 years of age) despite a recent focus on this age range. Following previous testing and validation, the 26-item iteration of the Children's Mathematics Anxiety Scale UK (CMAS-UK) for ages 4-7 years was further validated with 163 children (4-7 years) across two schools in the UK to test the validity and reliability of the items through subsequent exploratory and confirmatory factor analysis. The predictive validity of the scale was also tested by comparing scale scores against mathematics performance on a mathematics task to determine the relationship between scale and mathematics task scores. Exploratory factor analysis and associated parallel analysis indicated a 19-item scale solution with appropriate item loadings (> 0.45) and high internal consistency (a = 0.88). A single factor model of Online Mathematics Anxiety was related to the experience of an entire mathematics lesson, from first entering the classroom to completing a task. A significant negative correlation was observed between the CMAS-UK and mathematics performance scores, suggesting that children who score high for mathematics anxiety tend to score to perform less well on a mathematics task. Subsequent confirmatory factor analysis was conducted to test a range of module structures; the shortened 19-item CMAS-UK was found to have similar model indices as the 26-item model, resulting in the maintenance of the revised scale. To conclude, the 19-item CMAS-UK provides a reliable assessment of children's mathematics anxiety and has been shown to predict mathematics performance. This research points towards the origins of mathematics anxiety occurring when number is first encountered and supports the utility of the CMAS-UK. Subsequent research in the area should consider and appropriately define an affective component that may underlie mathematics anxiety at older ages. Mathematics anxiety relates to more complex procedures that elude the experiences of younger children and may instead be the result of number-based experiences in the early years of education.