Patient's question:
Here is the English translation of your text, with line breaks preserved as instructed and all Chinese content translated into English:"Hello, my baby is three months old now. Their head can straighten up, but they can't hold it up for very long and it still wobbles a bit, not well controlled. Is it possible they are calcium deficient? How old do babies usually become to be able to straighten their heads independently and skillfully without needing support? Thank you~!"
Doctor's answer:
Hello, 3-month-old baby, the head can turn freely as desired, and the eyes follow the head's movement, looking left and right. When an adult supports the baby's armpits and hips, the baby can sit. When lying the baby flat on the bed, his head can already be lifted steadily, the lower jaw and shoulders can lift off the surface, and the front half of the body can be supported by both arms. When lying alone on the bed, he will place his hands in front of his eyes to watch and play. When holding the baby upright by the armpits, he will lift one leg and take a step, then lift the other leg and take another step. This is an primitive reflex. By 6 months, his lower limbs will be able to support his entire body.