I think, like with so many things, it depends on the congregation. In the Presbyterian church I grew up in, the service followed the same order of worship week after week, and the music was primarily hymns. The choral music was a mixture of traditional and more modern pieces, but nothing that I, in retrospect, would consider "praise music" as the term seems to be used today. Children came to service with their parents through the first two hymns, and listened to the Bible reading, and had a little "Children's Sermon", then went downstairs to their classrooms for Sunday School while we had the rest of the service. Sermons primarily focused on God and His love for us, and our call to worship him and serve others. Sermons tended to be primarily topical with Biblical support, rather than explanatory of this or that Bible verse.
In the Presbyterian church I was married in, we had three services, and many more types of music. The youth group was very active with praise music, so when the Youth Minister preached, it was more of a "contemporary worship" style, while when the Senior Minister preached it tended to be more traditional. Children had Sunday School during service.
In the Reformed church my sister belongs to, the music is a pretty good mix of traditional and modern, and the focus of the sermons seem to be very solidly about God. Again, they tend to be topical (like on an aspect of God, with Bible exposition) and very scholarly. I'm not sure about the children thing with them, though, since I've only visited there a couple times.
In my current (Lutheran) church, the service is more liturgical, and the sermons more Bible-focused. Children older than 4 or 5 sit with their families through the service. Not Reformed, but fairly traditional. Some Lutheran churches, however, are very praise-music-oriented. So again, it really depends on the congregation, Reformed or no.
