My son is 3 in a week and watches video’s on his tablet, it is becoming more of a daily basis now but he watches a variety of things such as dinosaur songs and educational video’s such as counting etc. (he used to watch paw patrol on mine to start with). He basically loves anything that has dinosaurs or animals in so its a good way of keeping him occupied during more settled times of the day (mornings or after lunch).
I don’t see any harm in it, really I can’t see any difference between that and putting kids in front of the TV, it just holds their focus a bit more than having the TV on in the background. As long as they have a parental lock and you can keep an eye on what they are watching!