"I'm very pleased with the result but it's only half-time," the under 18's coach told liverpoolfc.tv.
"We are not thinking about the final and we still have another game to play. We have respect for Birmingham and there is still a lot of football to be played in the tie.
"I thought in the first 45 minutes we created good chances and scored good goals. We played a lot of decent football and we could have scored more than three in the first half.
"I was very pleased with the first 45 minutes but disappointed with our second half performance. Although we had good chances to put the game out of sight the goalkeeper made some very good saves. We didn't pass the ball well and the second 45 minutes wasn't good enough.
"We have got the second leg at Anfield but we have got to play for 90 minutes and not 45."