New born babies sleep for almost entire day but there sleep is not constant means they get up very easily and they fall asleep in the next second. But after attaining the circadian rhythm, there sleeping pattern get similar to adults. As they grow old there sleeping time gets fixed and they become less active during nights than in days. For a healthy baby they need to sleep for almost 20 hours during first few weeks of their birth. When they grow older there sleeping time starts to decrease during day and they sleep more in nights.
The below Infographic shows how much sleep does a baby required. Including baby sleep pattern segregated age wise, baby sleep room temperature, baby sleep problems and brain development of the baby.
Infographic Source: https://www.merinokids.co.uk/blog/baby-sleep-infographic