Over the garden wall frog
Greg's frog was watching over Greg and Wirt.1. They appear to be similar to Wirt and Greg in age, physical appearance, and nose style.(Wirt's triangular nose style is rare in the series, being only shared by a few other visible human characters.) The littler one even closely resembles an initial concept design of Greg that had him in a sailor suit.But there is one BIG difference and that is that these brothers are clearly having fun together, something that can not often be said for Wirt and Greg, EXCEPT when they are singing The Adelaide Parade on the ferry (and when Wirt starts tapping his cup with a spoon along to the rythym of Potatoes and Molasses, though that's not as blatant).To finish off this incredibly long theory, I will say that, yes, I know that the McLoughlin Brothers was a company that made books and games for children, but I think the theory is plausible anyway. I think these were the ORIGINAL McLoughlin Brothers. This supported, when he wakes up in the hospital and tells Greg that Jason Funderburker the Frog is "Our Frog".) If his last name WAS McLoughlin and he was considering Greg as a brother they would be the McLoughlin Brothers.But that's all "What If"s the REAL WMG here, is that Wirt and Greg are related to the boys shown in the theme song who are placing a toy version of the Frogland Ferry in a river. (And joining in in his interests, if HE was the one imagining the boat filled with frogs, but Greg is the one with the frog obsession.
Greg is actually his half-brother, and would not have the same name, BUT since this is seemingly the first episode where he willingly joins in with Greg's antics, and seems to truly care for him, it may be that he finally is considering Greg his brother.
Wirt's last name is McLoughlin(This is actually more like multiple WMGs condensed into one.)The Frogland Ferry is labled "McLoughlin Bros." If the Unknown is actually Wirt's Dying Dream he may have named the Frogland Ferry after himself and Greg.