I'm not exactly sure I'd call it an altar, it is more of a Home Altar Shelf.
But in our basement the children converted a little room into a place where they can practice saying the Mass (mostly for the sake of Altar Boy training... which we need to do for Merry and Pippin). We also use this for a place we can have our time for meditation each day. Each child up to age 10 spends 1 minute for their age in prayer. AFter age 10 they will spend at least their age in minutes up to an hour. When this picture was taken it was a little in need of cleaning but you get the idea. I have a set of stations of the cross for the wall that we have yet to put up.