When my son was in the nursery (our nursery goes up to age 3) I'd often take him in after the singing, and I'd pick him up before the offering. Then when he went to the younger children's class, they have their own music so he does it there with him, and we started going to the first service so I just take him before and pick him up after. We only started going to this church when he was almost 2, so I know the nursery a bit better and have let my daughter stay in there the whole time, and don't have her come with me at all. We go to a fairly large church and we have 6 nursery rooms alone that are geared towards certain ages/developmental levels, and then our children's ministry has puppet time and music time where they go with several classes, and usually that time reinforces a lesson they've learned in their individual classes. Even in my daughter's 18-24mo class they had lessons and crafts, as well as songs they'll "learn." (The teachers play them several times like during snack and while the kids are playing after the lesson, and each lesson is repeated/built upon during each hour, so they have repetition.) If my church just let the kids play with no lesson/music, then I'd bring them with me, but since they do have the lesson/music, I enjoy letting them go and learn and then being able to really worship without having to worry about the kids.