If you can call them first to let them know what you have so they can prepare. If not please leave them in your car if you are able to and go inside and tell them at the front counter. Doing this reduces the spreading of parvo if that's what they have.
Samantha's answer I believe is a good one for you but please make sure it's a cool day you can have plenty of ventilation in your car when you leave them in the car for cars heat up quick and puppy heat up quicker and if they do have parvo the heat will get to them even faster make sure you keep things clean so that if they do have it it won't be transferred to other animals thank you for asking how to take care of this problem
The humane Society
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