Our Children's film- Classification

We have decided to classify our children's film as a PG, as we would like to have more freedom in the content and the themes. Also, we think it may be harder to fill the criteria of a U, without using any discrimination/offensive themes. We may wish to explore more complex ideas, that a child of around the age of 8 would be able to understand without parental supervision. We wish to make references that an older audience would appreciate and understand.