Baby changes

Mummies, will baby sleeping pattern n time for milk change as they get older.. my little one is 4 months one.. previously he would drink finish his milk.. these days there‘a still remaining of 10-20 mls... just alil worries if he’s drinking enough.. Previously after milk he would stay up about an hr or hr half before he falls asleep.. now he stays up longer.. is it okay? How do u keep baby occupied when they are awake for Long hours.. Kindly advice mummies. Thank u!