When I was growing up, there was no such thing as a children's liturgy. We sat and fidgeted in our seats and tried to concentrate on the actual Mass.
Nowadays, the children's liturgy is a normal part of the life of a huge number of parishes. I've never been too sure how I felt about that. Was it really for the children's benefit, or was it just to get them out of the way while we concentrated on the serious stuff? Wasn't it better for them to stay with the adults as a sign that they were part of the parish family? Was the quiet removal of the small children from the church during the liturgy of the word a denial of Jesus' exhortation to "let the little children come to me"?
Or was it, on the other hand, a way to ensure that children actually got something out of coming to Mass? Were they learning to love Jesus more by hearing His message in words that they could understand and responding to it in their own way?
I've recently moved to a new parish, and I love the way they do their children's liturgy. As the children process out of the church at the beginning, the congregation sings "God be with you till we meet again". When the children return, just before the offertory, they all come to the front and stand on the sanctuary, holding up the work that they have been doing, while one of the catechists explains to us what the children have been learning. We then applaud the children's efforts as they return to their seats.
I think this is a great balance between ensuring that on the one hand, the children really feel part of the parish family and on the other, the message of the gospel is taught to them in language that they can understand, and attending Mass is an occasion for them to grow in their faith and not just to learn to sit still and get bored for an hour or so.