Self-control is the fruit of the Spirit. In other words it is the evidence, the legacy of the Spirit's work in the life of God’s people. This means we are talking about more than just physical or mental discipline. Any human can show control over these things. But only someone who is born of the Spirit of God can practice biblical self-control. This is why the biblical definition that Ruth Younts gives for self-control is vital for your children. "Self-control is the ability to say no to my wrong desires and yes to what God wants me to do."
This is why the gospel must be the center-piece of your parenting. As a parent you are to constantly teach your child to turn from the deeds of the flesh and embrace the singular fruit of the Spirit, which is manifested in the many ways that Galatians 5:22-23 indicates. No child, or adult, can practice biblical self-control in his own strength. The power of Jesus is the only means to be able to say no to self and yes to God.
Just because you don't know when God will save your child is no excuse for not proclaiming the gospel to them 24/7. God has commanded your children to obey you in the Lord. God has commanded you to teach your children his ways from your heart. You don't dare do anything else but teach and discipline your children to obey God's commands. You do this while pleading to God to rescue your children from the gates of hell. But you are never in neutral. You never withhold teaching them the gospel and biblical obedience because you are unsure of their spiritual condition. This is why teaching the good news of the gospel is a 24/7 mindset.