Yes, dilute shampoo or dish soap can be used to wash pests off leaves and prevent feeding. Here's how to dilute dish soap; the same proportions should work for baby shampoo:
Here are some of the pests that cause leaf holes:
Many of the pests have linked articles where you can learn about how to control them. The best way to identify the problem is if you can catch one of the critters in the act of eating your geranium's leaves. Keep checking it at different times of day. Then you can try to find a photo of the same bug online.