Without a doubt, that is way easier with a baby or toddler than a preschooler. When my kids were really little, they could be easily satisfied with cuddling, nursing, and a little toy to play with. Now that they are preschool and elementary age, the struggle is to keep them engaged with the service, and to begin to internalize it, while at the same time not bothering the people around them.
Step 1: Number your order of worship. This helps children know where they are and how long until the end. The service above had 14 different parts in it.
Step 2: Mark each section with these simple notations. An ear means "listen", musical notes mean "sing", an arrow pointing up means "pray", and a horizontal arrow means people are talking with one another.
Step 3: Make sure your child understand what he or she needs to be doing during each part of the service. Even with my preschooler, I expect full participation when we pray, sing, or have a "friendship" time. That means he stands when we stand, he bows his head and has "prayer hands" during prayer times, and he stands and at least tries to sing during the hymns. When the "listen" sign is next to something, it means he needs to be quiet and listen, but he can also do something else, whether that is coloring or reading his own book or even doing a jigsaw puzzle on my iPad (no judgment, please - it works, and we have Bible stories on there, too).
Step 4: Cross off each number as you finish it, helping your child follow along with the order of service and participate as you expect.
The great thing about this is that it motivates the child because he or she can see how many things will happen before the next "break" and can see exactly where we are in the service. And when we do this every week, the "flow" of the service is gradually internalized so children know what to expect and what is expected of them, until the day comes and you realize they are listening and participating on their own - not because you say so, but because their childhood faith has taken root in their hearts.