If the child was NEVER at the campsite then GGP and IR would have to lie to LE and say that he was there, because they were asked. But, LE continued to search. If either one of them said "I never saw him at all" this whole thing would have been conducted differently. Although I can't imagine it to be true, GGP might lie and take the position of being the one who last saw the baby, there is absolutely no reason for IR to lie about seeing the baby there - he didn't know the parents at all.
The dogs put the baby at the campsite and no where else. They only went to the reservoir because the smell of the cremains in the air drew them there. They didn't follow DeOrr's track/scent there.
He was taken from the campsite, carried away or in a vehicle. It is the ONLY explanation.