let grandparents take baby out while babysitting?

Lo
Am I overreacting? I've finally worked up the courage to let my MIL and FIL watch our 8 month old baby overnight (my first night away from her). Hubs and I bought tix to a concert to celebrate our anniversary early before he leaves for a 6 week army class. They now tell me (a few days before) that they want to take her to church Sunday morning so are asking for the car seat etc. This makes me a bit uncomfortable! I wasn't expecting them to try to leave the house with her barring an emergency or something. Am I overreacting?