Extracurricular activities

This summer our 3 year old took swim lessons and gymnastics classes. I wanted her to try some new activities and see if she enjoyed them. I also wanted to see how she would do respecting a teacher's authority and waiting her turn, since she will need to do that at preschool this fall. She did ok with both classes, and I think it was a good experience for her, but we're not continuing either one during the school year. In swimming she unfortunately got water up her nose during the 4th class, and didn't trust her teacher after that. So even though she could do the skills, she did a lot of whining and crying and acted afraid of the water. She enjoyed gymnastics a lot more, and loved all the jumping and different equipment. I liked seeing her persistence trying new things, and how she gained confidence each week. In the beginning she clutched the teacher's hand to walk on the beam, but now she will walk by herself with a huge grin. She doesn't always listen to the teacher, and still complains if the teacher scolds her, but it is cool to see the improvement.
Nevertheless, we won't be doing activities during the school year. She will be in school 2 days a week, and will have our playgroup for field trips. She is not asking to continue gymnastics, and I confess I don't enjoy sitting and entertaining her younger brother while she is in class. With the new baby coming any day now, I am trying to keep life as simple as possible. She's only 3, and I'm sure we have years of soccer, dance, and other activities ahead of us. What age did your children start extracurricular activities? How did you decide which ones to enroll in?