they also earn 0-5 xps at the end of each session.
This is issue was widely discussed here on the forums. Do a little research and you can see a lot of opinions about it. The main points are:
There is no too fast in DW; leveling up does not mean the characters are inherently more powerful or tough and does not mean that you have to come up with level scaled treasures or challenges. At level 11 characters can just change class, keeping whatever move was a signature of the character, and then just start over from level 1 (or retire and actually create a new character, but that's not the point). Even if a character should manage to level up once per 2 sessions, it's ok. Also, there's no imbalance in having parties with differently leveled characters within. Leveling up mainly allows you to come up with more cool ways to influence the fiction and that's all. As a GM, when a character levels up, I'm always very happy!
That said, when some of the characters arrived at level 3 if you feel, for some obscure reason, it was too fast, you can just adjust the xp requirement to level up. Instead of 7+level, maybe is 7+(levelx3); discuss it with your group to find the formula that best fits you all. But I strongly suggest to try the game as it is before.