The depth of meaning you receive from any kind of involvement is directly proportional to the level of commitment you're willing to make. I'm sure you've discovered this to be true in your work, your study, your volunteer involvements, your civic commitments, and your hobbies or avocations. The same is true for the church. Church membership is a concrete step you can take to deepen your level of commitment to the life of faith. If you want your children to take the journey of faith seriously, you're going to have to give evidence that you take that journey at least as seriously.
Kids have an uncanny way of picking up on how important something is to their parents.
One of the main things they watch for is the extent to which the parents are willing to commit themselves to the group or activity. If we drop them off for practice, attend only one or two games, and show little interest in what they are learning, then we shouldn't be surprised when they deicde not to go out for the team next season. Church membership should be the minimum level of commitment we would want to signal to our children. Our regular involvement in worship, study, and fellowship will give additional important signals to our children that we believe our faith is deeply important. If the faith journey is important to us, it can easily become just as important to them.