This phase doesn't last too long, so we should be patient with these little explorers. If a baby crawls by you, pick him up, maybe even hold him and help him focus on the service before returning him to his parents. In general, adults not caring for their own children should feel commissioned to help our swamped young parents watch over their kids. If you feel drawn to a particular child, ask her parents if you can help them mind her during church. Each parent needs to determine at what point their child has become too noisy.
Occasional noise is fine, but continual noise can be very distracting.
Some parents have found that taking the child out for making noise results in more noise because the child wants a change of scenery, or wants to play with toys. Some children also view this time alone with Mom as a victory. Children should not play with each other or talk to each other. Adults bending down to explain the service to children is fine, and may help them not be bored. The bookstore has a couple of good child-level guides to the church and the liturgy.