I have my spotted python in a 20L with, it appears, this same lid. Instead of running some type of wired thermometer probe into the tank, I just have digital thermometer/hydrometer combos inside the tank that are battery operated. You can find those on Amazon and I'm sure any big box store like Target, Walmart, etc.
They do make cage locks that will fit that lid, but like Nikkubus said, that does nothing for you to protect against the little one pouring a drink into it, or messing with hot lights on top. On top of that, even when these lids are secure they're not secure. You know already that it takes nothing to get that thing off. My two year old loves to see the reptiles so all of the enclosures are behind a closed door, but also up high enough that she'll be old enough to understand not to touch before she's tall enough to actually touch anything.