I wasn't familiar with Opinel, so I looked at some videos and reviews. The blade is evidently very thin and sharp, which is good for cutting string, tape, paper and food, but maybe not so good for serious carving or whittling. The blade on the #6 is less than 3", which may make it legal in more places, if that's any sort of concern. And the price is so low, it would probably be hard to find anything less expensive. I'm not sure how a kid or anyone would like that twisting barrel lock. It's slow and might seem "uncool" to a kid compared to faster opening and closing pocket knives.
I don't think even a 10 year old needs a blunt tip. That detracts from the usefulness of a knife, and would also detract from the full experience of learning how to use a knife safely—including the blade, the locking mechanism, the opening and closure methods, as well as the sharp tip.
I don't think a first knife will necessarily be lost easily; it may be treasured. I do agree that it's easier for a knife to slip out of a pocket than out of a belt sheath. A knife clip will help a pocket hold. The Opinel doesn't have one.
I have lots of knives, but they're all rather expensive, so I wouldn't recommend them as a first knife for a kid. There are literally hundreds of not very expensive folders that could be a first knife.
Here's a video from Knifecenter on pocket knives under $30: