Does anyone have an answer for this??

Mow.

The little oak trees aren't caused purely by the acorns falling on the ground, but by squirrels burying them. My experience is that they are usually buried one or two inches deep, and I just pull them up as soon as I notice them. It's much easier to pull them early than to wait until they are getting established. It's helpful to use one of those weeders that some people call asparagus cutters (the long tool with a "V" notch in the end). I've never had success cutting asparagus with them, but they are great for getting down deep into the soil and under acorns or pecans that are sprouting.

They are also caused by shoots off of shallow roots.

Mow.

And what you can't reach with the mower, hit with the weed whacker. If it keeps growing back, then dig it up. Manual labor with a shovel is the first tool in organic gardening!