For one to be a light in a dark place that person needs to first be a light. Thus while some may be able to argue for their older children being lights this argument is lacking when it comes to younger children. I would add that having worked with youth in the past I can truthfully say I have seen very few youth that would qualify for being the light God speaks of in His word. To be the light God has called us to be is a result of discipleship not simply a profession of faith, it is to be a reflection of the true light that is Jesus Christ. Children need to be raised to be lights and sending them off to the government schools does little else but indoctrinate them into the darkness the government schools spread.
Also, to send children of any age off to a system that is antagonistic to God and teaches along those same lines is to be avoided at all cost. The result of this abdication of the training of the children of believers is that the fear of God that wisdom begins (Prov 9:10) with is nowhere to be found. Instead children are taught that to fear God is not for the enlightened people we are today.
One may think they can counteract this government schooling with training at home but when children spend vast amounts of their time in the government school system it would take an inordinate amount of time to simply correct the wrong teachings and even more time to teach what is correct. With the small amount of time that parents spend in the home and even less time spent in discipling thier own children counteracting the government indoctrination seems highly unlikely.
So let us not send our children to spend large portions of their days in darkness. We need to take the commands of God to teach our children seriously and not abdicate that responsibility to the state.
You can also read a previous post by Voddie Baucham on this subject: Salt and Light
1) Christian Homeschooling and Charter Schools
2) What is the purpose of Christian Education: Part 1 & Part 2
3) Should the Government be involved in the Education of our children
4) Why are we so easily swayed by the money & items offered by charter schools?
5) Should not my children be in the public school to be lights in a dark place?
6) Why do we need to meet man’s standards for education?
7) Why do we need relief or a respite from the presence of our children?
8) Isn't how we educate our children a preference?
9) What if my husband says he does not want to homeschool?