I have been trying to grow wheat in my minecraft pe world and the wheat acts wierd

i was on my minecraft pe world and thought i should make a cake for my friend on it....i made my stone hoe and went out and made farmland i put the water in some spaces with my bucket and planted the seeds later i went up from mining and noticed some seeds were missing....i pretended nothing happened.some of the wheat was almost done growing so i walked back to my mining spot i then came back to collect my wheat and only one was fully grown the others became small again i have no idea what is happening though...