What materials can I use in a kids project to simulate simple cell biology?
This is seems like a good application of DIY sensory bags 

You fill a zip bag with hair gel, whatever objects you want inside, and food coloring if desired. We seal the tops of the bag with colored tape. 

We've filled them with toys, beads, glitter and whatever plastic or waterproof objects we have on hand. Even cut off pieces of drinking straws can work. In this case, whatever resembles cell anatomy. 

You can double bag them for more durability. They're able to withstand most handling, except for certain bites from toddlers (so teens should have no issue).