Minecraft – Can baby farmer villagers farm

According to the Wiki for the PE edition of the game:

On the Pocket Edition, they can ride other passive mobs, as well as other zombies and spiders.

This appears to be normal behavior.

Unless you have actually seen the villagers use the buttons for you iron door I highly doubt that they opened them themselves.

So there are a few resons why you might be actually facing this problem:

1. There is a spot where the villagers can hop into your farm. Those can be tricky to find, especially if you build fancy "natural" looking borders instead of just putting walls there.

2. Your door gets activated by a device that can randomly activate in a uncontrolled manor. Tis includes presure plates ( villagers running over them and then pathfinding to the now open crops), wooden buttons being shot with arrows from skeletons, weighted pressure plates by any random drop, or many more. My sugesstion is to just use a single stone button or something else that only a player can use, like a specific key card system.

Hope this helps.