Kate Gosselin -- Worried About Her Kids' Safety

The gunshot Jon Gosselin fired was more than a warning to a pesky paparazzo -- it was a wake-up call for Jon's ex-wife, Kate Gosselin ... who admits to TMZ she's worried about her children's safety.

Kate dropped a strong hint about taking legal action against Jon when we asked her about the gun incident outside Jon's cabin in the Pennsylvania woods.

Kate's 8 kids spend most of their time with her, but also visit with Jon.

But based on Kate's reply to our camera guy in NYC today -- "I'm doing what it takes to keep them safe" -- she's got something cooking ... perhaps with an attorney.