Help with discipline/willpower!

I love to eat healthy food, salads, fresh juice, plenty of fresh veg and fish are my main staples. i eat very little bread and excericse (cardio) on average for about 45min per day. I'm about 20lbs overweight. Nerver quiet lost all the weight after kids. My issue is picking at kids leftovers, a mini choc bar at that 4pm slump. I just find it difficult to stick to a specific calorie target. Always tend to sabotage the plan by picking and snacking. Help needed.