Q.Fixing a broken tree branch
I have a young Japanese maple that my son just broke a large branch off of. Can I tape/graft it back on? How do I do it successfully?

It's important to act quickly.
Try cutting 1" off of the cut end to expose live wood.
Fit together the 2 ends the best you can line them up.
Wrap the mended branch with breathable grafting tape.
Check the branch as summer approaches.
This can work with small branches, but if the ends have callused over the wood will not fuse back together.
Splintered branches generally will not regrow together.
Breaks that are at the trunk also are not likely to be reattached.
Larger branches, you may want to have a professional look at the tree.
https://www.gardeningknowhow.com/ornamental/trees/tgen/what-to-do-for-storm-damage-trees-repair.htm