I do not see that there is any "charge" to fight. Apparently, you have not been sued civilly, nor have you been arrested or charged with any criminal offense. It appears to me that the only legal issue here is who should have custody of your son. This serious, high-stakes legal matter cannot be resolved on this or any other website. If you are serious about regaining custody, you will simply have to hire a lawyer. You cannot learn how to accomplish this on the internet. Lawyers study and work for years to learn how to do it.
I suggest you consult a Round Rock lawyer who is certified in Family Law by the Texas Board of Legal Specialization. A link to the Board's website appears below.
Good luck to you and your son.