If you have hot sunny conditions, I would suggest a jade plant. There are many varieties. Some are very small with very tiny leaves, others will grow 3 or 4 feet tall and about that big around as well. The only problem you might encounter with jade plants are mealy bugs. Get a jade plant from a reputable nursery because the bugs usually they come with the plant. If you do find mealy bugs (look like little blobs of cotton fluff) the only way to eradicate them is to dip a cue tip in rubbing alcohol and touch each bug. Not easy, not fun, and they tend to be a recurring problem in that same plant.
Anyhow, 2 varieties of jade plant that are on a larger scale.
and
And this variety of cacti is very easy to grow in Calgary. I have a girlfriend and she has one, very nice plant, minimal care. Have a look at this one, it does not have the traditional spikey pokey things you are worried about. And nothing wrong with plants with those. Junior will only touch them once or twice, will not be an issue.
