What Causes Blood In Bowels Along With Redness Around Anus In A Child?

My son is three he somtimes has large bowel movements I noticed a little blood in one a day or two ago not a big deal today he went and he complained about it hurting when I wiped it. Looked at it and it was redder then normal all around. I put him in the tub and he said it was fine. Its still red though... I put some corn starch on it to keep it dry. What should I keep an eye out for? Im worried about worms and infection. Hoping its just irratated from using the bathroom.