My concern with a separate worship service for kids is that it seems to be both a surrender to their (and to our culture’s) insistence that they be regarded as a subculture, as well as an enforcement and perpetuation of it. It drives the wedge deeper into an already divided family and church while advocating the deeper unity of both! No such provision was ever made in Old or New Testament times for such a subculture as we Americans permit and encourage (and which the church now follows as it does all other things “American”). So far as I am aware, the only youth subculture mentioned in either testament, within the church proper (O.T. Israel in this instance), is found in 2 Kings 2: 23, 24. Biblically, It seems that evangelism (outside the church family proper) is generally, though not exclusively, a witness to adults who are then to win over and then disciple their children.
When I was a youth leader, not a single kid from outside the Church was ever won to Christ; all those who are walking with the Lord today, that I am aware of (out of many dozens of kids), were from Christian homes to begin with. I know that God sometimes works in reverse, but I think that the general principle endorsed in Scripture is, “Win the parents and they’ll win the kids,” not vice versa.
It would make an interesting statistical study to determine how many parents, worldwide down through the decades have been won to Christ as a result of their kids attending Sunday school, youth groups, Bible studies and VBS programs, etc. I think the real value of youth groups, camps, etc., is that they can be a subordinate supplement to the parents in their mandate to bring up their children in the nurture and admonition of the Lord. They have very limited value as a means of evangelizing families, though that does happen at times; we have had many non-Christian kids at camp over the years, for example, but I am not aware of any who have stayed true to the Lord, or been used by Christ to win their folks over to Christ. It is a reversal of the Biblical order, and the exceptions would prove the rule, it seems.
When Christian kids invite non-Christian friends to Christian events (or when churches do, likewise), this should then provide the church family with an opportunity to connect with, and evangelize the parents. That’s the mission field, and once their parents are won, the kids will usually continue to hang with you as well.
Very few people would agree with my take on this, but I am trying to be Biblical in my argument. That’s always the goal, anyway, but never easy to do because we are so steeped in our native culture! Joshua does not say, “As for me, I will follow the Lord; as for my wife and kids, it’s up to them what they want to do.” What he says is: “As for me and my house, WE will follow the Lord.”