The accurate and reliable assessment of visual function in infants and young children is important for ensuring optimal management of those at risk of abnormal visual development. Visual acuity is the aspect of visual function most commonly assessed by optometrists and can be measured in infants and children using appropriate techniques. Acuity measurements obtained using different techniques may show considerable disagreement and may mislead the optometrist when monitoring acuity development. It is important for the practitioner to appreciate these differences so that reasonable comparisons may be made between acuity estimates made using different techniques. With this in mind, we discuss methodological differences between some of the techniques used in visual assessment of very young patients and the effects those differences may have on acuity estimates.