The Declaration of Independence and the Constitution (our most important “founding documents”) were written by people who lived in a culture that was much more deeply influenced by Christianity than our own is. However, one can argue that there is nothing in either document that clearly reflects traditional Christianity. There are many things that could come from Christianity, but nothing that is exclusively Christian.
The Constitution does not make any appeals to God. The Declaration of Independence does, of course, have explicit and implicit references to God. People are given rights by “their Creator.” The US was entitled to an equal position with other nations by “Nature’s God.” The signers of the Declaration appeal to the “Supreme Judge of the world” to bear witness to their good intentions. They rely on the protection of “Divine Providence.” The first two of these phrases could come just as easily from Enlightenment deism as from traditional Christianity. The other two are more directly from traditional Christianity, but have little to do with the actual content of the document. They show that the signers of the document did want to express their faith in God, but do not show adherence to any particular religion. We can infer that they come from traditional Christianity, but they would not sound out of place coming from a follower of any other religion.
We know that the Founders lived in a time when Christianity was very strong. However, we cannot find any direct and exclusive references to Christian belief in the founding documents.