There are certain things you don't learn in medical school, like when should a baby drink from a sippy cup? This is a very personal choice for families. I've had patients that have been able to drink from a sippy cup at six months of age. Some babies just love it. A lot of babies love drinking from a regular cup at six months of age. A lot of times parents put a little bit of water or a little bit of the formula or breast milk in the cup and the baby loves to sip it down because they copy what their parents do.
The problem with a regular cup is that it spills 90% of the time when the baby holds it themselves. We have invented sippy cups. What are sippy cups? Sippy cups are similar to bottles in that the baby sucks from it and it has some kind of a nipple or mouth spout. Most sippy cups are spill proof, and that's what it will be marketed as on the bottle. Parents love spill proof cups because when the baby throws it down it won't get all over the floor.
The problem is that to make a sippy cup spill proof you have to make it very hard to suck. Often times if you try your baby's sippy cup, they have to generate a huge amount of suction to get some liquid out. I don't think this is very healthy for a baby's gums.
If you see your baby struggling to get the milk or the water out of the sippy cup, I wouldn't use that sippy cup. Some babies do very well with a straw. You can introduce a straw as early as six months. They'll often copy you when you drink from the straw, and you show your baby they can drink from the straw. Many of the sippy cup are straw-based and kids do well with them. The problem is that when one's with the straw, when they turn their head back, they can't get it because they're used to drinking their bottle like this. With the straw, the straw has to be at the bottom.
You can introduce a sippy cup as early as six months. Some kids are really dexterous and can do it on their own. Some kids are just not ready for a sippy cup until 18 months of age. That is totally fine. Between 15 months and 18 months of age, we recommend weaning the bottle and changing the baby only to a sippy cup or a regular cup.