This study will evaluate the efficacy of an intervention to improve quality and duration of self-regulated nighttime sleep (the amount of time the child maintains a combination of uninterrupted sleep, quiet wakefulness, and re-initiation of sleep without parental intervention).

The development of adequate sleep patterns is paramount to the optimal neurodevelopment, as well as to promote proper learning, develop memory and preserve cerebral plasticity. Factors that hinder sleep patterns can negatively influence the child's growth, neurological and motor development.

The investigators will conduct a randomized controlled trial within the 2015 Pelotas Birth Cohort. At the 3-month follow-up, children who sleep less than 13 hours per 24 hours (nighttime sleep and daytime naps) will be eligible for the study. The sample size was estimated at 276 children per arm. Nighttime self-regulated sleep duration will be evaluated at baseline (age 3 months) and at 6, 12 and 24 months using actigraphy and via a sleep diary completed by the mother. Following block randomization, mothers from the intervention group will be visited by a trained fieldworker who will deliver counseling on age-appropriate normal sleep behaviors, how to facilitate sleep onset and how to manage night awakenings.

Inclusion Criteria:

• To be eligible to the trial the child will need to belong to the Pelotas 2015 Birth Cohort, to be born healthy (newborns that needed intensive care after birth and with any congenital malformations will be excluded) from a single pregnancy at gestational age 37 weeks or greater, and to sleep regularly on average less than 13 hours per 24 hours (daytime and nighttime sleep) at three months of age (as reported by the mother). The information on child sleep duration per 24 hours will be gathered during the interview with mothers from the entire cohort, by means of the answer to the questions: "How many hours does the child sleep from 7pm to 7am?" and "How many hours does the child sleep from 7am to 7pm?"as well as number and duration of daytime naps, number of wake episodes during the night and how long it takes to the child to fall sleep after a nocturnal awakening.

Exclusion Criteria:

• Because the potential effect of the programmed maternal physical activity during pregnancy over the sleep duration or over the poor-sleeper-newborn answer to the sleep trial is not known, newborns to mothers that participated at the PAMELA trial will not be eligible to the sleep trial. The PAMELA (Physical Activity for Mothers Enrolled in Longitudinal Analysis) is a randomized controlled trial nested in the Pelotas 2015 birth cohort planned to assess the effect of regular exercise during pregnancy on the prevention of hypertension, pre-eclampsia and preterm birth. Eligible pregnant women between the 16th and 20th week of gestation are allocated into control group (426 women who are advised to keep their usual daily activities) or intervention group (213 women who engage in an exercise program, three sessions a week).

Also, because the sleep intervention will recommend a series of environmental improvements to ensure a restful sleep (no screen media, low noise and light), the intervention will be restricted to families living in households with at least one bedroom. Children in continued use of medicines that can alter the sleep architecture and/or lead to drowsiness, like anticonvulsivants, will be excluded.