I'm having the same issue; baby villagers not growing up visually, unable to breed, and so slowly my villages are depopulating. It's very frustrating as my seed only gave me 2 villages, I've done lots of building and mining that I'm happy with - but at this rate - I'll have no villagers in my world. I hope you can fix this before villagers can trade in this edition, many thanks.
I'm a noob to Minecraft - and only started playing a few weeks ago on Windown 10 Beta edition and have already lost almost all the villagers in two villages (the only two in my seed) to despawning. I've lost almost all of my animals, some horses with saddles, many dyed sheep. They just seem to disappear! I realise from reading this lengthy thread of comments that the issue has been ongoing for almost 2 years on pocket editions. May I suggest that when you do find a fix that you include a respawn for villagers for all of us who will have no villagers left by then - and who don't use commands? I've only ever played in survival on peaceful level. I'm so fed up with my game graft being wasted due to this issue, that I'm considering a) buying the full game instead or b) giving up Minecraft altogether - it's really disheartening to see quality game graft wasted. Please fix this - it's clearly bothering a lot of people.