"How can I protect my children from indoctrination within the public school system?"
Empower your children to be bold Christian witnesses at school.
While I defend Christian homeschooling and Christian private schools, I also know that these options are not available to all parents. Therefore, I support and applaud teachers and families in the public school system. No matter how our kids are educated, they will face challenges as they grow up. They need our prayers and support.
If you are a parent, be aware of the forces at school that seek to reshape the beliefs of your children. Stay attuned to what your children are being taught. Ask them questions about their day and what they are learning (dinnertime is an excellent time for these conversations).
If you hear anything that troubles you, don't jump to conclusions. Gather all the facts before taking action. At the same time, empower your children to be bold Christian witnesses at school. Pray with them and help them memorize Scripture. Encourage them to speak openly about their faith. Every day, when you send your children to school, ask for God's protection over them. Go into your children's bedrooms at night and pray over them as they sleep. Only God can perfectly protect your children against the attacks of Satan and this fallen world.