Yummy and scrummy - childhood terms for the taste of food. I remember using them when I was a kid. They're actually quite old - well, a hundred years or so - they're late 19th century - is the first time I've found a reference to them from 'yum, yum' - 'yummy' from 'yum, yum' - first, referring to delicious food, of course, and then to attractive people. That became a usage in the 1990s, which was quite fashionable for a while. People talked about 'yummy mummies' - that is, the perfectly-groomed woman who goes to yoga classes, stays slim, has clean children and has a four-wheel-drive. And other usages came in too - 'I've got a very yummy job', people might say, and recently, I heard somebody talking about somebody who had a very yummy blog on the internet - in that sense, it means, sort of, delightful and attractive, rather than delicious.
Well, 'scrummy', anyway became modelled on 'yummy'. It developed in the early 20th century some years later, again, originally with reference to food - scrumptious, you see, it's a derivation from that word, which means delicious. People talked about 'scrummy cakes' and 'scrummy recipes', and then, started using it as an adjective too, more than 'yummy' did, you know, 'that was scrummier', 'this is scrummiest'. I have heard 'yummier' and 'yummiest', but 'scrummier' and 'scrummiest' seems to be more common! Something 'sounds scrummy'. There are 'scrummy TV shows' now. The word, evidently, has moved on!