The Bible speaks of those who gain the whole world and lose their own soul. Their priorities were wrong and they lost that which was most valuable. Something similar is true of those who gain converts out there in the world but lose their own children.
This need to teach and train our own children first is evidenced in many places in scripture. In the OT, God's people were instructed to train their children at home, when they went out, and everywhere they go and in everything they do (Deut. 6). This requires not only a lot of time and effort, but it means parents have to be with their children in order to train them in the things of God. This has always been God's model for how children are to be raised by those who follow Him.
The New Testament includes the parable of the unfaithful steward (Luke 12) who did not properly care for the things entrusted to him and also speaks in the parable of the talents (Matt. 25) about the servant who did not invest what was given to him, but hid it and did nothing to bring an increase for his master. In these and other cases, the clear teaching of the Bible is that we are most responsible for those things which have been specifically entrusted to us. Of all the precious things entrusted to our care, the greatest is our children, who are specifically said in scripture to be gifts from God. If we fail in that stewardship, other gains we may have will pale in comparison. Yes, we should save the lost out there, but only after we save the ones God gave to us to train.
The need to train one's own children is also implicitly assumed in the qualifications for church leaders, who must be men with a reputation and record of not only remaining married and being self-controlled, but raising their children correctly so that they remain in the faith and are obedient to it (I Tim. 3). How can a man lead the church if he cannot lead his own wife and children properly? The clear indication is that he can't, which tells us not only that this is important, but of primary importance. The church leader must prioritize his own family so that they are properly led, before he can lead the church. And if even the church leader must prioritize his own family over the other work of the church, how much more the ordinary church member. We are all called to make our children our first mission field, with every other mission field secondary.
On top of that, women are specifically called to make their home and family their primary mission, even more so than men. Men must ensure that their children are in submission to their authority and being trained properly, but their wives are the ones who put most of the actual time and effort involved in this mission, because women are the ones called to be in the home caring for the children.
One of the major problems we have today is that too few have their family properly prioritized and they spend their time and effort everywhere but on their family. What we need is more Christian people who are teaching and training their children and building their marriages so that they can make a difference from a place of strength - a strong family that works together for God - and also be good stewards of what God has given them. This is not just about saving individual souls, though that is important, but about the intended purpose of the family to create, equip, and send out new soldiers to change the world for God. We can literally multiply our efforts to make a difference for Christ through properly trained children who continue the mission beyond us, in generations to come.