I don’t think Hergé was controlled so tightly that Abbé Wallez was saying, “Oh by the way, include a rhino being blown up!” – that came out of Hergé’s head in all likelyhood.
I think that in this instance we are dealing with a question of a more fundamental change in tone of the strip over the years, not the actual change in the social politics; that in effect we have in Congo
a paper version of the sort of non-naturalistic physical violence which was endemic in cartoons (especially animated) up until the fifties, when it started to be phased out. So Ignatz and Krazy Kat were lobbing bricks, Popeye and Brutus/ Bluto were putting each other through mincing-machines, and Tom and Jerry were doing all sorts of awful things, which usually ended with Tom looking like a coffee table with blinking eyes in the middle.
As the books progressed there was a sea-change, and Hergé largely abandoned the un-naturalistic violence, and made the books more realistic; what makes Congo
stick out is that a) it is unlike the later books, but b) it looks
like them because it was re-styled when it was redrawn.
Addition:I initially posted the following in another thread, but think now that it is better here.
In the recent coverage of the “Made in Belgium” debacle (see this thread), Hergé’s nephew has been quite outspoken.
He mentioned along the way in a couple of places that he enjoyed trips to his uncle’s office, and that he was always made welcome – so much so that he was never really aware of his uncle as anything other than his uncle, as opposed to a celebrity.
There was also a boy who was Hergé’s neighbour, who over the course of years amassed a collection of virtually every Tintin item going, and solemnly went and got Hergé to autograph them for him, which he did unfailingly and without complaint. There was a book published, show-casing his collection.
I therefore would avoid the heresay of Hergé being anti-child, and take the word of a child who knew him over second-hand reports.