One of the best ways to stay on track with your family's budget, is to curb impulse buying. Many people do this without even realizing it, and then wonder what happened to that careful planning that was supposed to balance income and bills.

The most common place that people impulse buy, is at the grocery store.  A good rule of thumb is never to go shopping when hungry.  Almost anything looks good when you haven't had a meal recently, and you're more likely to give in the appeal of a display or "special" for things that you might not buy otherwise.  Go shopping with a list and your coupons.  Don't sabotage yourself by giving in to cravings or convincing yourself that you deserve a treat.  

On the other hand, treats should be written into the family budget, whether those are food items, or an entertainment expense.  Financial budgeting is much like dieting for calories.  If you continually deny yourself all the good stuff, or the things that you like best, you're more likely to rebel and go overboard by gorging or spending to excess.

And of course, the classic safeguard against impulse buying is to ask yourself if you really need it.  Don't stand there and argue with yourself, and try to rationalize the purchased.  If you can't honestly answer "yes" immediately, turn and walk away.  If you really do need the item, it will still be there when you've considered your financial state and whether you can afford it.