Dark humor was always extremely popular among (Russian) kids from age 5 and onwards. I think most dark jokes I know I've learned before 14. ))
Sometimes it was quite dark. There was a series of jokes about WW2 concentration camps, popular among younger kids (I told quite a few of them too). I remember just one, but the idea was the same, just details differed. The prisoners in these jokes were kids, too. Their remarks were always told in very high pitched voices.

Начальник концлагеря объявляет:
- Сегодня мы будем есть котлеты!
- Ура! Ура!
- Ты, ты и...
- А можено я?!!
- Хорошо, и ты. Пойдете на фарш.

Concentration camp commander makes an announcement:
- Today we'll eat meatballs!
- Yay!
- You, you and....
- Can I?!!
- Ok, and you.. will be minced meat.


A bunch of jokes about dystrophics were good conversation starters in kindergarten and first grades of primary school (and they were not even considered dark). Only now, when I think that they were echoes of famines, they seem a little morbid.

Дистрофики в палате играют в прятки. Одного ищут, и никак не могут найти. Наконец он выходит из-за швабры.
Остальные дистрофики:
- Так нечестно! Мы же догововаривались за толстыми предметами не прятаться!