when my kids were younger and would go and play at a friend's house, it was easy to see how their older siblings played/reacted/treated my kids. If they were good, I would ask if they wanted to babysit. That was the best for us. We've also used the recommendation of friends, it was hit or miss. Actually had a college student once, never again, it was like she couldn't be bothered to interact with the kids. We paid good also.