In terms of physical, there is no good approach on the Macs since the newer ones are integrated in such a way you trash the assembly - the older ones are a glue and heat PITA. I wouldn't recommend tamper evident tape on the display directly either since it may damage the AG coating. Your best bet in this case is a thin webcam cover (NOT CHEAP TO REPLACE CRACKED DIPLAYS!!!) and tamper evident tape, or a fully SW configured block.
Your needs may be better served with a used PC, like an older business notebook. On many of these, the cam can be left installed with a BIOS block (disabled in BIOS and doesn’t show in Windows) or you can physically disconnect it since most PCs are more friendly to such a thing. It’s the nightmares like my FHD Touch E7440 you need to watch for - it’s built in such a way I can’t take it apart without ruining a $120+ USED assembly easily. If you do not want to deal with it being present at all, you can sometimes choose lower spec models like my E6440 pre-display assembly swap (i5-4300M/4GB RAM/768p TN LVDS LCD) and they usually do not come with it, or they were configured as such by the previous owner. Covid note: A lot of these are more ready then sometimes nicer “high risk” machines. Not easy to find one that’s easy since parents want one most people can get up and running if it isn’t possible to find one that’s setup.
Example of what to look for:
AVOID (IPS; panel looks really good, but the design makes camera removal difficult):
GOOD (poorer quality LCD, but easy to remove without damage):
However, be careful about displays - when I got mine, the display was bad (I got it cheap because of that). In my case, I found a HD+ (900p) webcam assembly was an extra $4 because of cosmetic damage I can live with for a better panel without having to muck with the cable. Yes, the E6440 LVDS has different cables, while the iDP has one (iDP has better panel upgrade viability). However, it is a horrible machine if she needs to carry it (thicc+~4.5lbs).
CAUTION: On the business machines, you need to be a little careful about Computrace being active. If it is, check with Absolute SW and provide your proof of purchase and they’ll help you remove the tracking from the machine, but nobody can change the persistence module - not even Computrace. But it can be “neutered” with a POP and an eMail.
In terms of the cut: Don't cut it - it makes restoration hard for you to reverse, or if someone buys it secondhand hard for them. Disconnection or removal is usually sufficent, especially for someone who isn’t there technically. Cutting it devalues the hardware to tinkerers. I personally hate machines someone ripped the cam out AND cut the cable. If I'm dumping the assembly (or at least the back lid), I’m still annoyed but I’m willing to consider it a “no harm no foul”. The issue is if it's in nice shape and I do not need to replace the back lid, I'm looking at a 1-2 hour repair to reverse heavy handed parenting. If possible, save that cam module and the parts so when you sell it or she's older, it's quickly restored. A bag of parts is still annoying, but everything is there to undo the original removal.