We spoke to each other on another forum about this problem.
Incidentally, I think that sticking to one theme for 30 minutes is more than enough, lends some coherence to your lesson and doesn't confuse them. I also think you can link themes and vocabulary up to stories. So, no, they are not too young for storytelling - they are the perfect age for it and it's a great way to present vocabulary and make it meaningful for them.
You can choose a classic song like Old MacDonald and teach vocab for animals, the farm, the farmer and farmhouse, for example. You can use animal noises as a base for a lot of games and teach the song before finally getting your hands on a simple book telling the Old MacDonald story to read with the children after a few lessons.
Note that I said "read with them" and not just "read to them" because if they have learnt that a cow goes "moo" in English, they can make the sounds when you are reading.
You can get at least four or five lessons, if not more, out of Old MacDonald or Little Red Riding Hood.
Contact me through my blog at Teaching English Lesson Plans
for a quick chat about a lesson plan if you need more help for a specific lesson. I'll be glad to help.