It all depends on the individual children and ages.
We have 5DC, only the youngest is of that age now at 7.
She has one of her friends come over once or twice a week after school for tea and a play until around 6.
Luckily these kids are all lovely and they tend to just play with Lego/dolls/draw/dress up/imaginary games. Also, I know their parents so are familiar with the DC and have no qualms about telling them off etc.
We’ve had a few rogue kids visiting over the many years though. Ones that tipped all the toys boxes out, ones who behaved like dicks to our DC, ones that whinged about everything for no reason.
These kids generally weren’t invited back and our DC got put off the friendships after witnessing how they were in our home.
We’ve always told DC that they have a responsibility but any mess created and us parents will help but they tend to try and manage any destructive ‘tipping every single tiny toy out for malice not play/destroying stuff’ behaviour as they know it can’t just be left.
Bloody love it when DD’s mates come over now. They keep each other occupied and are generally delightful and funny.
The big kids (2 adults and 2 teenagers) have always been welcome to have friends over and their guests are 99% amazingly polite and kind (remind me a bit of Kevin and Perry being very polite to the other parents 
)
Over the years of having play dates/friends round we’ve realised that it’s important to:
a) try and know the kids and their parents to see if they (hopefully) have similar values and rules to your home
b) set out clear expectations with your DC regarding behaviour and tidying up etc.
c) tell DC that if they’re not happy with what the other kid is doing then feel confident to say no or tell us.
d) put away annoyingly destructive exciting things like Nerf guns if you don’t want or can’t be arsed with refereeing.
e) give the kids some slack but at the same time don’t be afraid to tell them off.
f) if you suspect the kids will dick around when it’s time to get shoes/bag and ready for parents to extract then don’t be afraid to say you’ll drop them off home (if possible). This has saved a lot of resentment and frustration when we’ve been knackered are kids aren’t listening.
g) Drink shitloads.
h) realise that other families might not be able to facilitate play dates after school in the week due to work etc. I totally don’t mind that, having friends over benefits my DC so I don’t see it as tit for tat.
Of course parents can take the piss but having healthy boundaries and not being afraid to say ‘no’ is vital.
Honestly @JemimaPyjamas if this kid’s visit or any others turn out to be more hassle than it’s worth then just chalk it up as lesson learned not to invite him again. At 9 they should be keeping each other occupied playing and making life easier for you.
Chin chin! 