I like that, because it uses the stereotype promoted by their advertising campaign where an elderly and kind-hearted grandfather was seen to give his grandson a Werthers Original, as a way of bonding between them, which no doubt resonated with many of the viewing public and their own relationships with their grandparents. As such, the Werthers Original brand became synonymous with elderly relatives giving sweets to their younger grandchildren. The first bit of the joke is therefore entirely innocent, as it is expected that an elderly gentleman might distribute Werthers Original to younger children.
However, the second part utilises the nature of said Werthers Original, namely that they have a smooth, creamy taste. It also relies on the stereotype that elderly gentlemen can have paedophilic tendencies towards younger children, the most well-known example in popular culture probably being Mr. Herbert from Family Guy. Taken in this context, getting children used to 'something creamy' in their mouth is construed as the elderly gentlemen preparing the children to receive their ejaculate, most likely by means of fellatio in an act of paedophilia, which when contrasted to the innocent nature of the first phrase, provides a discernable 'shock value'. The 'shock' and surprise however, later turns to humour when the construction of the joke, the element of surprise and the taboo subject it broached is appreciated.
All in all, I liked this joke, and would certainly welcome more contributions from the poster.