Be clear about your expectations and set your limits clearly. Define what you will and will not tolerate right at the beginning.
Things to determine at the beginning with the teen parent are:
Times of arrival and departure.
The things you require the parent to bring such as diapers and wipes, extra clothes, and updated medical forms.
Be sure to let the teen know what the consequences are for not meeting your expectations. Be concrete in your explanations and don't "beat around the bush." Focus on your goal and what you want. Do not be angry, but tell it straight and in objective terms.
Explain your rules and why you have them.
You will want to keep your communications short. Teens are busy and need you to be right in step with them. They do want feedback, but they want it fast.
Always be positive, honest, and be clear about what you want or need. For instance, you might say,
"When you're late, your child keeps looking for you. It's important that you come on time."
"Your baby needs five clean diapers each day. If you don't bring diapers, you will have to pay me $2.00 for each diaper that I have to supply and use."
"Try to slowly put your baby's jacket on. She needs you to stay calm, even though you are in a hurry."
"Lower your voice, and just talk with me. Tell me what is bothering you."