Divorce is stressful. There is a lot on your plate between maintaining your job, dividing all the assets, figuring out living situations, and determining custody agreements. Even if you were the one that asked for the divorce, there is some sadness too. It's a major chapter of your life coming to an end. It's easy to forget how much your child's life is changing too. While doing your best to keep all the sadness and hurt from them, trying to keep their schedule as normal as possible, and never bad mouthing the other parent, your kids are still stressed too.
Even if your kids knew everything wasn't happy in your marriage they still won't understand why it's happening. They will internalize it. They will spend a fair amount of time wondering if they could have stopped it. It is so important to keep the lines of communication open with them. What details you reveal are at your discretion, but some form of, "mommy and daddy grew in different directions, and while we don't love each other anymore, we both still love you very much," is important. Kids need that reassurance, and often.
Little kids can sometimes hold very unrealistic expectations; such as asking if you can all still live together. Their entire world is often centered on us and how we behave. Keep that in mind always. The way you talk to your soon to be ex in front of them, and how you talk about each other to them, will be remembered. As much as you want the divorce to be over or as angry as you may be, the kids don't need to see it, not now. When they are older, late teens to adults, they are more capable of having a conversation about how you felt, but now they not only can't understand, but they will internalize.
Divorce for kids means their entire way of life has ended. Consider (if possible) a civil friendship with your ex until the kids are older. If your kids play sports, are in band, or anything other event you go watch, if you and your ex can't sit together your kids will have to choose who to run to first. That kind of decision can be crushing for them. Their time with their parents is now limited. They will have different rules and expectations at both houses. They will have a lot of their own emotions tied in as well. As hard as this is for you, it is just as hard on them. Make sure you acknowledge that to them, and try to help them through it too.
Your kids will survive your divorce, but they will need your help to do it. Don't minimize their suffering (by accident or by choice) because they are young, and don't compare it to yours.