"Can't parents just watch over their children", that's a Shibboleth for detecting people who are not parents. Why, it's as easy as writing bug-free code on the first shot. While doing all the other everyday chores of course.

All the toys that used coin cells here at my house had screws on their compartment. You can have all the theories or best guesses about such legislation, but it surely gave us a massive peace of mind that the cells wouldn't pop out at the most inconvenient time or completely out of sight. By the way, try to keep 100% of your attention for 100% of time with
twins. Kids have all the time in the world to figure out things, and a simple compartment door with no specific locking mechanism would be surely opened by them. Besides, this phase lasts until 2 or 2-1/2 years old, to which you are able to teach them better to not put everything in their mouths. By the age of 3 my girls were already working with the screwdriver and loved it!
Reversing the tables, if you are an adult that cannot be bothered to buy a set of precision screwdrivers or ask someone to do it, you shouldn't buy these toys. The spring on the batteries compartment would surely be another problem in case these are opened unexpectedly - batteries flying everywhere. For the loose screw argument, that makes sense but there's a reason why you do this away from kids or at the time they are napping - being an item that is replaced only so often, that is a doable procedure.
For the other things that need to be opened and connected more often, such locking mechanism surely irritates me. I've had the medicine containers frustrate me a few times, but these were also effective during this hand to mouth phase (on the occasional dropped container).
Also, several US plugs can have a very tight fit (especially the more commercial/industrial looking types) and they are relegated to be used in extension cords and other applications that are connected for long periods. I never used the chubby european plugs/outlets (UK, Germany) but, if they are hard to insert/pull as they look, then no thanks. However, I find it ironic how the US bashing about their "unsafe" plugs is the norm in these types of discussions, but in a somewhat similar concern the number of incidents is brought up as a reason to ridicule this. Last time I checked the number of electrocutions was rather small...
All in all, I think that bringing this to the table generates the discussion and, at least with the already severely regulated toy market, this is just one more fib to add.