Children have the right to participate in child protection investigations. Although research suggests that participation is related to positive outcomes of children in the child protection system, children’s participation is not always facilitated in practice. Therefore, it is important to validate tools that can be used to further investigate children’s participation. We examined the psychometric properties (i.e., reliability, internal validity, and external validity) of the Meaningful Participation Assessment Tool (MPAT), which measures the degree in which child protection professionals enable children’s participation in child protection investigations. The MPAT is based on the Model of Meaningful Participation (Bouma et al. 2018) and distinguishes three domains of children’s participation in child protection: 1) informing, 2) hearing, and 3) involving in decision-making. It consists of 13 items. We validated the MPAT based on data from 292 child protection cases. We concluded that the MPAT was reliable, internally valid and externally valid. The MPAT’s reliability was reflected by substantial Cohen’s Kappa coefficients ranging from .63 to .92. The Mokken scale analysis revealed a strong scale of 8 items (H = .70, Rho = .89). Items on seeing and hearing children about child protection topics seemed relatively more easy to achieve compared to items on providing children with information, which suggests that child protection workers may struggle most with informing children. Lastly, we concluded that the MPAT might be externally valid because we found higher MPAT scores for subgroups based on child protection institution, age, and gender, which was in line with our expectations.