In general, the school lunch program is a good thing for the people who consume the lunches, but it might be a bad thing for the government.
The main point of the school lunch program is to make sure that students have good food to eat at school. This is particularly important for children whose families may not have all that much money. Those students might not get the nutrition they need and might suffer from lowered performance at school as a result.
A secondary point of the program is to help farmers. The program was started in part as a way to encourage consumption of domestically-grown produce. Supporting American agriculture is another pro.
The cons have mainly to do with the government. First, this is a program that costs money. All of the food needs to be bought and made at taxpayer expense. The public must also pay to administer the program. Second, the program brings up issues of federalism and of governmental control. In essence, it allows the federal government to dictate what our children will eat at school. Some people would argue that this is an infringement on state rights.