I LOVE the idea of a feely bag! If you can find something that feels really unusual it could really capture their imaginations! Have you been told the ability of these 4 children? As you only have twenty minutes you could do some group writing rather than getting them to write lots themselves - discussions about what they think it could be, where it came from etc. You just have to have a good idea in your mind what you want from the children - is it to use adjectives/WOW words or something different? If you haven't been given any objectives it can be what you want it to be - just make sure it links to Year 2!