Our kids had two phases in which electrical outlets were interesting. These are crawling infants who find outlets near the floor interesting. This phase lasts about 7-8 months. After that, they start walking and the stuff down there becomes uninteresting, then the stuff up top becomes interesting.
A little later comes the reaching up to the light switch, preferably to the roller shutter switch. This phase lasts at least another 9 months, more likely longer.
As with all safety measures in the household, they are only a makeshift solution. The only true protection is education, teaching that fingers have no business there. Because you can hardly childproof the entire house and the houses of others, like grandma and grandpa, aren’t secured anyway. Besides, you plug in and unplug few devices in the secured rooms, so the "hassle" with simple locks turns out to be less effort than one might think beforehand.
A bag of locks costs €3, of course you can spend many times that and replace outlets. Edge protectors for coffee tables, cabinet door locks to the point of unusability, stair gates ... all exist, but everyone has to decide for themselves.