4 Months to 6 Months

If baby is awake and unhappy/fussy/crying, first assume she is hungry.
If baby seems full, put her down on her back to make sure. If she cries when this happens, offer more food and if she eagerly eats more, it means she was hungry.
If baby refuses to eat and won’t stop crying no matter what you do, call the doctor.

Please read our guide on preventing iron deficiency, which also discusses vitamin D intake.

Most babies are not ready to start pureed foods until 4-6 months of life. Please read our guides for starting solid foods to find out if your baby is ready to start solid foods and how to go about that process.

All babies spit up; most of the time they swallow it down without you noticing. As long as baby is feeding well and stops crying when fed, this should be ignored.
Just a little spit up or what seems like the whole feed, 2 minutes or 2 hours after the feed, curdled or not curdled, this is normal as long as baby is feeding well and stops crying when fed. If baby won’t stop crying no matter what you do, call the doctor.
The frequency of spit-up increases between 2 and 6 months. This is also normal.
Babies do not suffocate on their spit up.

Many parents believe their baby is teething between 4 and 6 months of life, because they do a lot of drooling and chewing on their fingers.
In reality, putting hands in the mouth is an important developmental milestone which also causes drooling. Neither one indicates the onset of teething.
You will know your baby is teething when you run your finger across the upper or lower gums and feel sharp teeth poking through.
This happens between 6-15 months of life.
Please read our guide on teething for information on understanding and managing teething.

Tummy time, all the time. If baby is awake and quiet, we recommend tummy time on a firm, flat surface.
Baby needs two things for development at this age: Tummy time and hearing words from the people she cares about. Why not do both at the same time?
Interactive activities with your baby during tummy time are the most effective use of your play time together.

*The following assumes your baby was born on time. If your baby was born early, please read our guide to development in babies born early.

By the 6 month visit it's important that you to have seen your baby roll from his back completely onto his tummy.
The only way to make this happen is tummy time.
If this hasn't happened by 6 months, we usually refer to physical therapy for extra help getting on track.

Some babies get flat heads, which may require a helmet to mold the head back to normal.
Tummy time whenever baby is awake and quiet.
Avoid excessive time in equipment such as bouncers, swings, floor chairs, etc.
- Spending too much time here can contribute to head flattening.
Alternate which arm you hold baby with.

The dreaded "4 month sleep regression" gets a lot of press, and, understandably, causes parents a great deal of anxiety.
In reality the 4-month sleep regression comes down to one thing: your baby is overtired when you put him down. He is either awake too long between naps or his bedtime is too late. Usually, it's both.
Please see my guide to sleep in the first year of life for more information.