Background: Most young children (0–3 years) attend formal childcare in Denmark, many of them fulltime. Yet recent reports of the quality of Danish childcare centers have shown that in more than one-third of nurseries, the interactions between caregivers and young children (0–3 years) are of “insufficient” quality, which constitutes a risk for affected children’s well-being and development. Effective interventions to improve childcare providers’ interactive skills are necessary. Methods: In this randomized controlled trial, we test the effectiveness of the Caregiver Interaction Profile training, which focuses on improving six core interactive skills: sensitive responsiveness, respecting children’s autonomy, structuring and limit setting, verbal communication, developmental stimulation, and fostering positive peer interactions. We will recruit N = 200 childcare providers from nursery groups in Copenhagen (n = 100 training group, n = 100 waiting-list control group). Our primary outcomes are childcare providers’ six interactive skills named above, observed from video-recorded interactions in the nursery groups. The secondary goal of our study is to test whether the training boosts children’s social-emotional and linguistic development. To this end we aim to recruit N ≈ 500 children from participating childcare providers’ nursery groups (n ≈ 250 training group, n ≈ 250 waiting-list control group). We measure social-emotional and linguistic development with various standardized questionnaires, filled out by parents and childcare providers. Discussion: If the training is effective at improving childcare providers’ interactive skills, then this will be an important foundation for implementation efforts, such as offering the training as part of the educational program of childcare providers. Future research should also evaluate whether the Caregiver Interaction Profile training is effective for childcare providers of older children (3–5 years) in Danish kindergartens. Trial registration: This trial is registered at clinicaltrials.gov as “Testing the Effects of the Caregiver Interaction Profile Training on the Interactive Skills of Daycare Providers (CDP)” with registry ID NCT05654116. Registration date: 12/01/2022.