I started my kids off by bringing them to Shabbat afternoon mincha. It’s a short davening, and they got to see the sefer Torah. Then they graduated to coming with me on Friday nights. I davened (in the winter) at a nearby Chabad shule. While the shule took a break between Mincha and Kabbalat Shabbat to learn Tanya, I did parsha and alef-bet with the kids. My wife brought them on Shabbat morning after Musaf; when I saw they could handle longer periods, they came with me to shule for the entire davening. I loved having them with me, and they sat quietly with a few books they brought with them.
To this day, my kids (who are now older teenagers) remember “Abba’s Rules”:
1. Abba leaves on time for shule. If you want to go, you have to be ready to leave with Abba.
2. In shule, you either sit next to Abba or are in a group. There is no other choice.