Professors Snape and McGonagall polyjuice as the Dursleys, and see Harry off through the barrier at Platform 9 3/4. The Malfoys are already on the platform and Draco hauls Harry off to a compartment, introducing him to his friends Crabbe and Goyle. Or perhaps that should be; introducing him to the sons of his father's retainers, Crabbe and Goyle.
Their first "adventure" is some time later when a tearful Neville Longbottom turns up looking for his toad. Harry remembers a spell for summoning a familiar in a book of his father's which is in his trunk. So they haul the trunk down, find the book, and Harry encourages a doubtful Neville to try it.
It works to perfection. Neville is delighted, Draco is reluctantly impressed, and they all settle down for lunch.
In 2011:
And in 2020: