What are some babysitting activities that will gurantee me the job?

I am probably going to babysit 3 school-aged girls, ages 8, 9 and 10. They will be coming to my house a few times and the mom wants to see if they get along with me or not. I need a couple of REALLY good activities that will make them happy and entertained and gurantee me the job. I want them to want to come back again and again because this is a full time job so I'll be spending a lot of time with them. I was thinking of organizing a scavenger hunt, but this would be awkward for the mom who needs to talk to me. How about making playdough? Decorating cookies? Taking a walk? Help me out! I need the perfect babysitting activity(ies).