Several equations to predict muscle power (MP) from vertical jump height (VJH) have been developed in adults. However, few have been derived in children. We therefore aimed to: 1) evaluate the validity of existing MP estimation equations from a vertical countermovement jump (CMJ) in children and adolescents, and 2) develop and validate a new MP estimation equation for use in children and adolescents. We measured peak MP (Watts) and VJH (cm) during a CMJ using a force platform in 249 children and adolescents (9-17 years; 119 boys). We compared actual (force platform) to predicted (twelve existing prediction equations) MP using repeated measures ANOVA and estimated bias using modified Bland-Altman plots. We developed a new prediction equation using stepwise linear regression, assessed predictive error using leave-one-out and ten-fold cross-validation and externally validated the equation in an independent sample (n=100). All existing prediction equations demonstrated some degree of bias, either systematic bias (mean differences ranging 178 W to 1377 W; 8%-64%), bias at the extremes or interactions with sex. Our new prediction equation estimates MP from VJH and body mass: Power (W) = 54.2*VJH(cm) + 34.4*body mass(kg) – 1520.4. With this new equation, there was no difference between actual and predicted MP (0%) and negligible differences (0.2-0.9%) in R2 and root mean square error between our observed and cross-validated sets. Actual and predicted MP were not different in our external validation (p=0.12). The new equation demonstrates excellent validity and can be used to predict MP from a CMJ in children and adolescents.