Not to condone any particular evangelistic tactic but you have to realize that for some of these people, they believe that until their child commits to Christ that they are doomed to hell. Imagine if you are a parent who truly believes in the doctrine of hell and of one particular plan of salvation. If you are a loving parent then you are going to try anything you can to make sure that does not happen.
This situation is worse in branches of Christianty that have a particular physical ritual that must occur before you are "saved". The pentecostals for example believe that you must be born again of water and the spirit before you are saved as evidenced by speaking in tongues. The water baptism is easy but then you have parents beside themselves if their kids have not yet spoken in tongues. Some kids fake it, some condition themselves into believing that they do it, some kids may even actually do it (who knows?). The point being that the pressure is there from the standpoint of the doctrine and parents are just trying to do the best for their kids so they don't end up in hell.
Of course, biblical creationists are committed to belief in God's written Word, the Bible, which forbids bearing false witness; --AIG (lest they forget)