A special note should be made of the problem of eating too fast or too slowly. When your child consistently eats much too fast, gently encourage him to take smaller bites, not to take another bite until finishing the previous bite, or to chew more thoroughly before swallowing. Gentle reminders from time to time usually are enough. If not, firmly insist he eat more slowly. If the problem persists, you may want to consider requiring he stay at the table for twenty minutes or so regardless of how soon he is finished. Be sure the adults at the table are not eating too fast, since the model set by adults has a lot to do with the eating habits of children. A good rule is no one (including adults) leaves the table until everyone is finished. It also helps to talk more slowly at the table, to plan meals for a time when there are no competing activities or TV programs. Try to create a relaxed and peaceful atmosphere at the meal table.
Your child who "takes forever" to eat presents a different problem. She may be avoiding food she does not like, or she may be experiencing some dental problem interfering with eating. It is more likely, though, your child has developed a habit of playing with her food. If there is no dental or physical problem, it is appropriate to insist your child eat. Next, be sure your child understands there is no dessert if she does not finish at approximately the same time as everyone else. Finally, and somewhat extreme, you can set a reasonable time limit for removing all food from the table, including your child's plate, and see to it your child receives no snacks later on. If your child is eight or nine and the problem persists, three or four nights of having her food removed from the table is usually sufficient to improve the situation.
Whether your child eats excessively fast or excessively slowly, do not get into a power struggle with her over the issue. Simply respond by encouraging a change in behavior and then insist on a change, combined with controlling the availability of snacks and the amount of time to eat. Eventually, most all children modify the time required for eating.