You can do it. Google finegardening.com, propagating soft wood cuttings. In Summer, have started Forsythias with cuttings just shoved into ground. Probably can start Crapes the same way. It helps if you dip cutting in water and then root hormone. Maybe other Forum members can add some info here.........

Propagation is relatively easy if you have the right equipment! First have a sterile pair of gardening shears and try to cut a branch with as many nodes as possible- 4 or 5 is fine. Strip off all but the top few leafs. Dip the cut end of the branch in rooting hormone abd depending on the type of plant, woody, soft wood, succulent, place directly in soil or in a cup of water. Place the cuttings in a sunny place and water often. NOTE: some cuttings need to scab over before being planted! Do a little research and it should be easy as pie:) I do this with almost all of my plants!

I have done crape myrtle, roses and boxwood of the ones you mentioned. Roses sometimes work, sometimes don't for me. The crape myrtle and boxwood worked well. Other things that work well are forsythia and euonymus. After dipping in rooting hormone, I stuck the stems into potting mix and draped a plastic bag over the top to conserve moisture. Just be sure it doesn't stay damp enough to rot.

If you're not pressed for time--that is if you have continued access to the plantings at your childhood home, a surer method would be to tip layer. This works well with the three I mentioned. To do that, bend a low branch down to the ground, scrape a bit of the bark off on the bottom side, being careful not to damage the top, dip the scraped part into rooting hormone, bury the branch and lay a rock or brick over it. This is best done in late winter or early spring. Wait a year and take a look. The branch should have rooted. If so, remove it and you have a new plant. If the crape myrtle has no low branches, you can root prune by stabbing a spade into the ground a couple feet from the plant in one spot. Often the root will send up a sprout at this spot which you can remove in a year or two.

One of my earliest "cuttings" was sticking a broken forsythia branch in the ground. We had accidentally broken it off, & I did it so grandma wouldn't notice. Few months later, she noticed a new bush was growing. I guess they'd fall under the "so simple a 5 year old can do it" category.