Can animals spawn?
The new release of Minecraft: PE features baby animals. Will these animals eventually spawn in existing worlds, or will my kids (who have built some rather elaborate structures for the Pocket Edition) have to start over?
It appears to be the case that animals never spawn in older versions of PE; are the baby animals a change to that, or are they just a new thing which could be running around at the beginning of a game?
Unfortunately, your kids would have to start over in a new world in order to get the baby animals.
According to the update changelog on the Minecraft Wiki, baby animals only will spawn in new worlds, in the same fashion as adult animals spawn.