Children's development during early childhood affects their well-being and educational success, but there are few reliable assessment instruments available. The aim of the study was to develop, pilot and validate an e-assessment instrument for assessing five-year-old children's development in cognitive processes, learning, language and mathematical skills. The tablet-based instrument was piloted in Estonia in 11 kindergartens with 122 children. The teachers guided the children one by one over several days. The instrument was validated using teachers' evaluations of the sampled children's skills. The results showed positive associations in expected skill areas supporting the claim of the instrument being valid for assessing young children's development.