Four months is the golden age of baby's brain development and fine motor development, so it is good to learn science in small steps. My baby can skillfully take out tissues and handkerchiefs from the box when he is more than four months old, and he is quite flexible in turning over by himself. You don't have to milk or coax when you sleep, just listen to the good night music of small steps and you can fall asleep by yourself. Every time I look at the sleeping baby, I appreciate Xiao Bu's company for several months. Baidu knows more.