Hello, My Pug puppy Casper is of 4 months. One day his rectum comes out with blood while doing stool, i take him to the Vet he told me there is nothing he can do after stitching and blocking rectum. He also told me not to give much food to the puppy?

The most common reason for a rectal prolapse is usually straining from either diarrhea or constipation for some reason. After a repair you usually want to try to keep the stools a little more middle ground, softer than normal but not too soft, while they regain the muscle tone and the stitches disolve. If they strain they are likely to pop the stitches and it's back to step one and more stitches.
Did they run a fecal and check for parasites or bacteria that may need medication? If not, you would want to do that but it may also be the consistency of the stools contributing if he is popping stiches. If your pup is pushing much at all from looser or harder stools, then it is more likely the stitches aren't going to hold.
I would not feed a human baby cereal. The main ingredients usually consist of a corn or grain product, a milk product and often sugar. High quality dog foods do not contain corn or low quality grains (low digestibility and nutritional value, used as more of a filler and food allergy). Most dogs are lactose intolerant and milk products containing lactose in quantity or as a regular part of the diet aren't recommended and may make them ill. A human baby cereal isn't proper nutrition for our doggies either.
You might discuss feeding a good quality canned food for dogs and/or maybe even mixing in something like a bit of rebound at first to add moisture if you need to soften things up a bit and/or possibly adding a bit of canned pumpkin (not pie filling) if you need to firm things up a bit and how much since you don't want too much too soon either way.
I hope you guys get it all figured out soon and everything stays where it's supposed to. Let us know how he is doing please. Good Luck.
http://www.pugs.org/ q4267050.html#a3103682 http://www.dogfoodanalysis.com/dog_food_reviews/ 
http://www.bornfreeusa.org/facts.php?more=1&p=359 
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