I usually judge the book not the author. Some of my childhood favourites are considered awful people by todays standards (rightfully so in most cases), but as long as the books are well written and enjoyable I can separate art from the artist.
David Walliams books are awful, at least the three I read were (I used to read the books before reading them to dc when they were younger, to check they were good/interesting/appropriate).
Unfortunately, like many of the celebrity books for children, they were published (and sold well) just due to his name. I do wonder how many J.K.Rowling's there are out there that would be unlikely to get a chance now, because all the big budgets go to 'sure thing' celebrity authors.
Hopefully parents stop buying the trash, actively avoiding anything with a random famous name stuck on it. Then we might start to see many more high-quality, fun books that could become classics for children.