Ulfa, Maria, et al. “The Effectiveness of Playing Ball Stimulation to the Gross Motor Development of 24-36 Months Children”. Jurnal Ners Dan Kebidanan (Journal of Ners and Midwifery), vol. 6, no. 2, Aug. 2019, pp. 107-11, doi:10.26699/jnk.v6i2.ART.p107-111.