Hi Cambria,

You mentioned that your daughter is stealing the candy late at night when everyone else in the home is in bed. That suggests the candy is being kept low enough for her to reach, or in an unlocked cabinet that she can access. Consider removing her ability to access the candy (either by removing candy from the home or keeping it locked up). This will at least remove the object of her stealing, while you explore the cause(s) of the behavior and effective parent responses.

Here is some information on Education.com to help you understand why your daughter may be stealing (and what you can do about it)...

When Children Lie and Steal
http://www.education.com/reference/article/when-children-lie-steal/

My Child Is Stealing
http://www.education.com/reference/article/Ref_My_Child_Stealing/

The Lowdown on Lying, Stealing, and Cheating
http://www.education.com/reference/article/Ref_Lowdown_Lying/

Learning Right From Wrong
http://www.education.com/reference/article/Ref_Learning_Right_Wrong_1/

It's also important to understand what may be happening for her developmentally at this age...

The Fantastic Four-Year-Old
http://www.education.com/reference/article/Ref_Fantastic_Four_Year/

Assessing the Development of Preschoolers
http://www.education.com/reference/article/Ref_Assesssing/

I hope these resource are helpful to you. Please also talk to her pediatrician -- he/she may be able to offer guidance specific to your daughter.

I'm going to take the "health" view here, rather than the child behavior view. Personally my solution would be to have no candy in the house. That's what happens in our family.  I've actually never seen candy hanging around in any of my nieces and nephews homes. There's no reason to have it: it just helps develop carb cravings, feed a developing sugar addiction (Which you daughter seems to have already developed), and makes other sources of sugars unappealing. Leave a bowl of grapes, cherries, clementines, cherry tomatoes, small and appealing veggies and fruits, etc., on the table. For snacks, offer a variety of fruit and dried fruit, vegetables ... they're all sweet too! By doing this, you solve the problem and help your child integrate good eating habits now. When we have family gatherings, I see all the kids go for the finger foods, veggies and dips of all kinds, fruit and cheese, and they really, really enjoy them. It's what they grew up with. So, instead of seeing it as a problem of "stealing",  view it as a developing carb craving and health issue, and offer a tasty and healthy alternative.

4-year-olds have small stomachs and don't eat a lot.  Therefore, if they do nor get healthy snacks between meals and shortly before bedtime, they might start to sneak food.  

Sweets satisfy hunger and provide a sense of gratification, so your child chooses what comforts her.  To prevent her from sneaking sweets at night, provide her with a healthful snack before bedtime, such as oatmeal, cheese and crackers, or apple sliced with peanut butter.  Also, removing temptation from the house would not be a bad idea!

Please read The Power of Healthy Snacks
http://www.pluggedinparents.com/index.php?option=com_content&task=view&id=20&Itemid=0

First, I would put the candy in a place where she can't get it. Second, I would offer a healthy snack before bed that tastes sweet--like graham crackers with peanut butter or 1/2 bagel with cream cheese and a little jam, or even a single piece of candy (you could even do sugar free). To deal with the roaming at night issue, you could put latches on the kitchen cabinets and certainly one the exterior doors (we installed the chain locks at the top of all the doors that lead out of the house, so our daughter couldn't reach them even with a chair). I would not put soap in her mouth. It is behavior that borders on or is emotionally abusive, and it doesn't deal with the problem and if she is sneaking candy because she is hungry and then getting soap in her mouth, this could lead to food issues and/or eating disorders. You can discuss a reward/punishment system with your daughter. If she stays in her room at night, she can have 1 piece of candy before bed, but if she gets up and tries to get candy, then not only will she not get candy, but something else will be taken away (like no tv time the next day).