This is one area that spending more money should not be an issue. There are various types of car seats you can choose from. Keep in mind that it is better and safer to choose a car seat with a 5 point harness system.
You can buy them separately or as part of travel system strollers. They are smaller and usually can be placed on top of strollers. You use them rear facing in the car. They are handy but babies outgrow them quickly, somewhere between 3 to 6 months. They are normally designed to handle baby weight up to 20 lbs or height of 26 inches. If you are interested in infant car seats, make sure not only they are the same brand as your stroller but also a perfect fit. (I recommend that you buy a travel system stroller which includes car seats with the stroller).
Meanwhile if you are bottle feeding, infant car seats can become handy at nights or when you are alone and suddenly have to feed two crying babies at the same time. You can strap both of them in their infant car seats and feed them at the same time!!!! That scenario alone may be worth getting them for newborns.
These car seats stay in your car and can be used both as rear and front facing according to the weight and age of your baby. The important factor to consider is the 5 point harness system. They are usually usable until your child reaches 40 lbs.
This type of car seat grows with your child. They can be used as both rear and front facing. The difference with convertible is that they can be used up to 100 lbs depending on the brand. This type of car seats converts to booster seat as well. Now I am not sure how many of them in the market can actually work for so many years without any wear and tear?!
Once your children reach 40 lbs then they can graduate to booster seats. They usually come in two styles: seat only – no back or seat with a back.
Our choice: We chose a travel system with infant car seats. For some reason it came with one car seat and we had to add one more to it. Besides the feeding tip, imagine taking the little ones to the doctor's office without them? They are very handy.
For normal car seats, we recommend Britax. Britax is known as the Cadillac of car seats. We used one for our older child who is 4 now. The seat is in great condition and I am using it for one of the twins. Not even a tear in it! We bought another Britax car seat. The only tip we can give is if your kids are prone to sweating, choose the Britax with denim fabric.