I have a few trees that I have taken from cuttings. They are rooting nicely but the leaves are still the same size as they would be in the wild and still attached to the parent tree. Since I am still new to this, how do I get the leaves to stay smaller and look like they are on a bonsai tree? Does the process work the same for all trees? Or is it different for each one? Please help me!

A lot of leaf shrinking depends on the species. Some will shrink, some won't.

Leaves already grown won't shrink. What I do with elms is take a longish new twig starting to grow that has little leaves close to the main branch and cut it back where the leaves start to be big. After a couple years of this the tree learns to have small leaves only. The parent tree has leaves maybe 3 cm long, and the bonsai elms have leaves maybe 4 mm.

Note that this will take years.

Awesome, thanks for the help! Ive been learning that this is a patience thing, but I'm loving the process!

Leaves do not shrink, the next set of leaves will be smaller. But this is years away for these cuttings, they have to grow first

In general, as your bonsai matures (First you have to grow a trunk and basic branch structure) you will get more and more small twigs. This in itself results in smaller leaves. One of the final stages in bonsai development is frequent thinning and even nar complete removal of all leaves in mid-spring, rsulting in a new flush and more twigs with smaller leaves.

Thank you! For tree species that do not lose their leaves in winter, I would just cut or pinch the leaves in order to remove them mid-spring, correct?

Keyword is “partial outer canopy defoliation”.
Can’t be done with ALL deciduous tho.