The study, published in Nature, comes from a survey of more than 700 families in the United Kingdom. Their findings is summarized as follows: "Every additional hour of tablet use was associated with 15.6 minutes less total sleep (on average, 26.4 minutes less of night-time sleep and 10.8 minutes more of daytime sleep)." Unlike television, screen time on smart devices actually increases the amount of naps during the day. These are the effects on children under the age of three in this survey. No correlation is found between screen time and the number of awakenings at night.
The authors, however, are quick to note that in a previous study they made on this same group of children, the use of touchscreen devices is found to correlate with early development of fine motor skills:
Clearly, a balance is needed so that young children benefit from screen time without its possible deleterious effects. The authors conclude, "Together, our findings emphasize the need for a more in-depth understanding of how to maximize benefits and minimize negative consequences of this modern technology."