is there a way to limit spending on apps. I got charged for things that I didn't know I bought.

There isn’t a mechanism to add a spending limit, but you can ensure that both App and in-App purchases require entry of your AppleID Password to confirm the purchase:

Settings > [Your Name / AppleID] > Media & Purchases > Password Settings >

[When Purchasing] Always Require Password - select

[Free Downloads] Require Password - set to ON