Kittens should actually be fed 3 times a day until they have finished growing, not twice, it is too long between feedings for them.
I have seen the difference between kittens who have been fed a diet of poor quality kibble and high quality canned/raw and it is amazing. Kittens need a lot of moisture and high quality protein to grow healthy bones, muscles and organs.
I feed my foster kittens Kitten Wellness, canned in the morning (left out all day while I am at work) and raw feedings after work and at bedtime. I have not had a problem with food going bad doing this. I have had a vet comment on the amazing health and muscle mass my foster kittens have compared to kittens fed Royal Canin.
If you find Kitten Wellness canned too costly, then even Wellness grain free canned, Natures Variety Instinct, or Ogranics by Nature (better yet, a raw diet) are all very good foods that your kittens will thrive on. Try it for a month, I guarantee you will find a difference in them and will never go back.
I have added links so you can compare the ingredients between the food:
http://www.bynaturepetfoods.com/prod...nedcat.php#ttl
http://www.naturesvariety.com/instinct_cat_can
http://www.wellnesspetfood.com/cat_w...n_chicken.html
http://www.hillspet.com/hillspet/pro...tProducts.hjsp
Have you ever seen a cat in a corn field eating corn?