There are two important things you might like to know BEFORE you watched this film.
Firstly, as it has already been pointed out here, don't switch off when the closing credits start rolling: after them, there is an important scene that provides some closure (dots the "i"s and crosses the "t"s). Why the film has been edited this way is anyone's guess but it is rather unfortunate.
Secondly, not many people know that there is a prequel to this film (with the same leading actors), which provides a background story and some depth to this one. It is a short (30 min) film called O otci (About a Father), 2017. If you watch this, you'll know why the relationship between one of the leads and his partner's mother has been strained (the fact is briefly referred to in the opening sequel) and you are likely to have a more multidimentional take on the characters too.
If your expectations are right, you are likely to enjoy this film. You shouldn't expect a high-brow drama, it is a 'feel good' story, which should be very much familiar to the Western audience under the guise of 'Christmas films' while the Eastern Europeans of a certain age will immediately recognise the all-to-familiar 'social fairy tale' screen feature of the Soviet era. Basically, it is teen adventure fiction, and there is nothing wrong about it at all. You don't have to be 16 to enjoy it properly but, as it is with, say, Gulliver's Travels by R. L. Stevenson and Treasure Island by J. Swift, the younger you are, the more you'll enoy them. The closest analogy to Kam motýli nelétají will be J. Verne's Les Enfants du capitaine Grant, better known to the English-speaking audience under the title In Search of the Castaways, though. In fact, it feels like a lot of inspiration for the film comes from this particular Verne's classic oeuvre.
As the laws of this genre dictate, the quest and the adventures take priority. The characters are mostly one-dimentional and, as in any fairy tale, the baddies are just bad while their opponents are just good. You won't see much of a character developments in these stories either, unless the inner conflict between the good and the evern better in each of the 'good' characters is considered. So, by the end of the story, the only transformation you'll see is the already good ones becoming even better. The moral is simple and straightforward, the story-telling is untaxing and relaxed. It is a perfect family movie, which is both safe and highly enjoyable to watch with your kids who are 14+.
The latter posed a certain problem to the script: the coming of age angle of the story would have been more natural if the protagonists had been 14-16 but as they were 19 in the film, some aspects of the younger protagonist's inner drama seemed rather anachronistic. It also created some (very minor) difficulties, as far as the plot is concerned: at 19, the young protagonist is already a young adult, so having his parents summonned to the school because of his academic failures looked odd (would have been pretty normal, should he still be 16 or 17). These minor hickups won't spoil the entertainment though: after all, it is just a modern fairy tale, so don't expect too much plot rationality and realism (a chest of highly practical treasures fortuiously found just at the right time, perfectly drinkable water from the underground pool, an average-sized rucksack that still magically contains a full wardrobe and a pantry, etc). After all, you don't look for realism and rationality in, say, Harry Potter and the Philosopher's Stone or any of the films for the young audience produced at Barrandov Studios in 1970s-1980s, do you?
The film has been shot well and the actors are doing a good job, mostly. Given the natural lack of depth in the characterisations, they don't have a particularly tasking job to do. Jiri Vojta, the older main lead, is doing the best with the material he has. Unfortunately, the other main lead, Daniel Krejcik, is a much weaker actor. It is not that, being 28, he had to play a 19 year old. It is his acting abilities that lack: displaying emotions doesn't come easy to him, nor the result is natural or pleasing. He is not completely disasterous though - he just could and should have been better at basic acting. As he isn't, his protagonist comes out rather unfavourably creating an unintended impression that the actual reason for the universal dislike to Daniel is his being artificial rather than different.
Overall, it is a very enjoyable film, perfect light watching for a family evening.
