jam and cream sponge cake with light dusting of icing sugar on top

Safe, yes. Nutritional value: almost 0.

 

If you spoil them with treats they may turn up their noses at their balanced feed. It's easier to prevent this issue than to correct.

 

You may feed that to me! Yum!

But if you make a habit of feeding your flock high sugar and starchy treats, you are setting up their crops for possible yeast infections.