Be careful with sweet feed. I personally wouldn't be giving it to youngsters. Oats and hay (with alfalfa/lucerne preferably as it contains a good balance of protein and calcium - perfect for young, growing horses).
You can get very good balance pre-mix youngstock feeds, my youngster has been on Prydes Biomare since he was weaned, and has done exceptionally well on that, with some lucerne and ad lib meadow hay.
Just avoid the sweet feeds if possible, it's like feeding a human baby a bucket load of sugar!