I have 3 files, 1 parent & 2 child

When I give statment like :-

sele parentfield, child1, child2 from parent, child1, child2 where parent.code=child1.code and parent.code=child2.code

It shows me double records i.e.

if a parent record is having 2 child records in each file, it is showing me 4 records, instead of 2. (values are getting repeated).

Any Ideas/suggestions ??