On the most basic level, what we dream represent either what we fear, or what we wish. That's if we believe in dreams meaning anything. Some dreams certainly appear to be little more than mental excrement.
If Frank dreams of his youngest son being abducted, I suppose it simply means Frank is worried about his son being safe, which is every parent's very normal concern. Maybe Frank is afraid that for some reason he might be unable to provide safety for his son. For example, if Frank were to go on a week-long business trip, this might trigger the, again normal, fear that something might happen to his son during this time. Or maybe the son stands as a symbol for something or someone else close to Frank. In no way does Frank's dream appear crazy or abnormal.
Regarding symbols: for example, teeth are a symbol for food (obviously) and money (less obvious). A dream in which ones teeth fall out could mean a fear of starving or financial problems.