Is it harder to ref U-littles?
Yes, harder to referee Ulittles in my opinion. But I'm not sure the above game qualifies, to be honest. What age group is this video from? U11? U12? Also, as the post above references, we don't exactly know what you're getting at.
In this video, there was a clear foul, and it was whistled. Was it misconduct and deserving of a yellow card? Up to the referee really. For me, it depends. There's a talking-to coming for sure, but issuing a yellow card depends on what has happened before, the temperature of the match, and the skill level of the players. Was it just an isolated incident of frustration, or something that had been brewing? Etc. This type of foul is not so common at Ulittle level, and much more visible in the olders. In the Ulittles, I wouldn't show the yellow card. But even in the olders, where this foul might be much more inflammatory, I wouldn't necessarily classify it as misconduct.
Back to your original question, I do think Ulittles are harder to referee as there is can be a big difference in skill level and experience. Additionally, there is still a degree of clumsiness, and, when mixed with inexperience, there can be a number of shockingly bad challenges. Generally speaking, I like to deal with younger players with a stern talking-to, which is why I would lean towards no card for your video. Just my onions, though.