Hi Marcia!
I wish you could see the smile on my face right now. When my son was 2, we adopted a kitten. That first Christmas, he was obsessed with the tree, and it was adorable, albeit frustrating. I ended up bolting the tree to the wall, using a sturdy cup hook and some fishing line. That way, if he did climb the tree, at least it couldn't fall over.
Put the breakable ornaments at the top where they're less likely to get batted around, and some nice, unbreakable ones on the lower branches that are within reach of the kitties. You can also attach ornaments with twist ties so they're more firmly attached to the tree.
What else can we do? Cats will be cats.
Thanks for bringing me some wonderful memories of our beloved kitty, King Bing, The God Cat, gone for over 15 years now. What I wouldn't give to have him here with us this year, batting and climbing to his heart's content!