My twenty-one month old has already hit the terrible twos. I think she hit them when she was 1! She is very opinionated and, let me tell you, she does not like these cups. We used Avent bottles because they were the only ones we could get her to use that didn't cause nipple confusion for her. We thought these would be a great transition since they were basically the same design. The assorted pack comes with multiple sizes and a variety of spouts. Some of the spouts are silicon which we hoped would be a great transition as our daughter got used to the more rigid plastic spouts which are also included. This was not the case. She does not like any of them and will defiantly throw the cup down if we try to give it to her. It may just be my daughter, but the cups just don't work for us. In addition to my daughter's issue, we found that these cups leak if not threaded perfectly. Make sure you have a nipple brush to clean them. They come with a plastic guard that keeps the cup leak-proof. Once you take that guard off, the only way to clean the spout it with a smaller sized nipple brush. They are impossible to clean otherwise. Ultimately, we switched to cups with a straw and they work wonderfully.