Not starting them off on the way of faith.
The Bible says: Start children off on the way they should go, and even when they are old they will not turn from it (Proverbs 22:6).
If you are a Christian, how will you respond to God if He ever asks you why you didn’t talk to your children about Jesus? Why didn’t you take them to church? Why didn’t to show them the value and satisfaction of serving others, of loving “thy neighbor”? What will you say? Will you blame the government, your many occupations or your ex? If you say you are a Christian, your first responsibility is leading with example. Just in case they don’t understand you, you must speak to them and teach them what the Bible says about God.
Leaving children to grow up with no beliefs, and thinking he or she will make a decision for Jesus later doesn’t work all the time. Putting excessive pressure on them to “behave” as Christians when they are not may also hurt them. There is a balance, and if there is no balance, you are still responsible for talking to them about Jesus Christ.