if you trust you can use them to be your reference, you of course should include them in your application materials. In that case, you will have to get their permission and be sure they will say good words for you. If they agree to be your reference, it usually can be very helpful, as internal recommendation is usually highly regarded. You will need to call them to be sure they are willing to be your reference. If you do not think you have worked with them long enough, maybe it is better not to mention about this, as they may feel uncomfortable to serve as a reference for you.