There are many 12+ months breakfast cereals available in UK supermarkets that are suitable for vegans. Ella's Kitchen and Organix make a few types (please check ingredients as could change) that can be served with Alpro Junior soya milk, but I don't give this very often as it really doesn't contain enough good stuff. When I do serve this, it's with a good teaspoon of ground flaxseed on top.
Breakfast doesn't have to be complex - fingers of toast are a good quick fix. Small has things like mashed avocado, peanut butter or low salt yeast spread (with added B12). Porridge made with coconut oil, raisins and ground flaxseed (for fat & Iron) is also a firm favourite. I also make a breakfast version of Sneaky Dad's Pudding in a smoothie as I know it packs in lots of goodness for the day. I usually offer a drink of soya milk (Alpro or formula) and fruit fingers as well.
If you have a bit more time then you could make all sorts of things - I sometimes make breakfast protein muffins (I'll post the recipe during #veganmofo) that Small and I eat together. We also enjoy pancakes, English breakfasts, smoothies, muffins.........
What do you give your vegan kids for breakfast?