I have a application and it works :

have one primary table with 1200 people Information
and I have aprox. 30,000 records in a child table and is very
slow consult the child table with a relation, when i need sum the
amount of the child table for each record in the primary table, the system is very slow, i have index on IDCliente in my primary table and
i have an Index in my child table Idcliente for make a relation and the relation works ok, but my sysetm is so slow, what I'm doing bad?
how can a give more speed to my application?

Sorry for my English