I've got a house full of little ones. Lent is a challenge. How do you convince a four year old that giving up a good thing is a good thing? Well, in all honesty, that's hard to do. We simply use the "In our family" explanation. It goes like this, "In our family, we don't eat candy or sweets during Lent." Then we go from there. We explain why we offer it up and all the other useful stuff that will serve to explain matters when they are a little older, but in the meantime, they accept this line in the sand difference between our family and others.
Being Catholic, we like to involve all the senses in our daily walk with God. We've talked with the kids all year about how our sins hurt each other and especially how they hurt God. To make this point concrete we have a Crown of Thorns during Lent. It sits on our dining room table next to a tin of toothpicks. When we hurt other family members through carelessness, spitefulness, or harsh words, we apologize and then put a thorn in the crown. We leave the toothpicks in our crown until daddy and mommy make it to Confession, when we get home, we all cheer and clap as we remove all the toothpicks and start afresh. The kids tell each other to be good and it becomes a challenge to keep the crown free of thorns for as long as possible.
Now as you can imagine, by the end of Lent mommy and daddy are being reminded very frequently to go to Confession. Also, the kids have gotten the hang of rebuking the mote in each other's eyes while tripping over the logs in their own. Naturally, with this exercise comes the accompanying exercise in charity and self-examination (that's what's known as the "flip side" by those old enough to remember 45s at sleepovers).