Our altar is placed on the kitchen's marble case. We moved to this new house some months ago, and I haven't found yet a better place to put it, and sincerely, I think that the kitchen is one of the best places for it to stay. I love my little kitchen and the shelf where the altar is placed is perfect in size for me, since I don't have many objects over it. Kitchens are very powerful places for witches, and I spend a good time over there preparing goodies for my two men. My son loves helping me when I'm cooking, so it's a warm and cosy room to be, with good vibrations. There's this amazing site about magickal kitchens that I can't take my eyes off since I learned about it!
Usually my altar is very simple and plain, like the first photo above. When we're celebrating sabbaths, I add some colored lining and images, according to the celebrations, and Lucas is always adding something, like little rocks and dried leaves he finds in his walks - the two wooden wands on the right of te photos was chosen by him. In Ostara he dyed some boiled eggs to decorate it, and in Beltane he chose the images to put on the wall (I think I said before, we follow the Southern Hemisphere Wheel of the Year, so Ostara was held in September, and Beltane, in October - now we're waiting for Mabon to arrive).
As long as Lucas doesn't mess up with the objects, I let him touch everything that's displayed - he's always very respectful - only being careful when the candles are lit, of course. He loves changing the Goddess water every morning, and he often spend some seconds in front of it many times of the day, just watching, as he says. For him it's part of our lives, because he's used to it since he was a little baby. And that's exactly how I wanted it to be.