Momma, you are courageous to come here and admit that you are spanking and even more courageous to want to change.
Like you, and like many moms here, I was not raised in any sort of a "gentle" manner, and I very much want to raise my children in a different way. I've been reading and reading and meditating and reflecting and practicing, and these are the things that I've learned that I think may be helpful to you.
First, I'd like to recommend the book
Becoming the Parent You Want to Be by Davis and Keyser. It is a great, albeit lengthy, read on this topic. One of the most valuable things I got from it was help identifying my values and the things that I want to pass on to my kids, and how the decisions I make as a parent pass them on.
Gentle discipline seems to mean different things to different people. BUT from what I've distilled, there are two "offshoots" of this idea.
1. Utilizing a rewards/punishment system whose rewards are positive and whose punishment is "gentle." Gentle in this manner generally means no corporal punishment but rather the use of time outs and other parent-generated punishments that do not cause physical harm to the child. This system of discipline is similar to what you're doing now, but it requires that you draw new boundaries with your punishments, so that you are not hitting and perhaps not yelling.
2. Utilizing "unconditional" or no praise/no punishment parenting. You hear alot of terms for this, including democratic discipline. This line of thought is that you do no kind of "manipulation" to your children, utilizing no praise, no punishment, no threats, and no bribes of any kind and rather focus on the needs of your kids and yourself to guide you. This is a radical and very powerful shift in thinking and acting that accepts that, if your kids are "misbehaving" they are not doing anything to hurt or bother you but are rather trying to get their needs met. Its the job of the parent to decipher what the needs are, identify what your needs are, and find a solution that meets both. It's not permissive, limits and boundaries are still very important. It requires a great deal of work and thinking. Like I said, it's a radical shift in thinking that has taken me some time to get my mind wrapped around, but once you do it, a whole new world will open up to you.
For example, your kids broke into a room and spilled a ton of paint on the floor. What needs were they meeting in so doing? To expend energy, since outside play isn't easily accesible to them? To connect with you, in any way that they can? To connect with one another? To lead? To follow? To figure out what that goo is and what it does on the floor? All of the above? Using this approach, you don't punish for the behavior, you let your kids know that they broke a limit and that you don't appreciate it, and find a different way to meet those needs--a way that meets your needs, too.
If you are interested in this approach, Anthony Wolf's
The Secret to Parenting is a very quick, digestible read on the subject that is full of real-life examples and directions for doing this well. He's got some (in my opinion weird) psychology behind his methods, but the methods themselves are excellent.
Look here: http://joanneaz_2.tripod.com/positiv...esourcecenter/ and here: http://www.awareparenting.com/english.htm for more on this subject.
Also, Playful Parenting by Lawrence Cohen is a great read on this subject--and I imagine with a house full of rambunctious kids, you'd get a ton out of it.
Gentle discipline, like all good parenting, is a path you walk every day. I fall down alot. And get up, dust myself off, and try again. And again, and again. Treat yourself gently and forgive, forgive, forgive.
Namaste.