These examples aren't normal though.
In ten years of having a fairly open house to the kids' friends I've only met one child locally like that. His mum told me that he really wanted to come to ours to play with my dc3 (they met in the local playground and were playmates of convenience). I said ok and she sent him over(alone on foot) the next day and drove past waving 30 seconds later (away from her house). He was an absolute nightmare. He didn't play with DC3 at all but went around picking all the electronics (belonging to me, DH and dc1 and dc2) up and demanding to use them, tried to go into my bedroom and those of dc1 and 2 repeatedly despite being told they were off limits, and demanded to watch TV, play x box and be fed, all within 30 minutes of entering the house. Even he didn't help himself to good or open the fridge.
I told him he was here to play with DC3 and he commenced repeatedly telling me he was bored. I told him to go home then. He then went to play with DC3 for about ten minutes then came back to demand X box as a reward.
I told his mum when she came to pick him up and she said yes he can be difficult 
It was a huge shock as almost every other child I've had round, amounting to 40 or 50 children over the last decade, has been no trouble and it's been easier to have extras than just my own as they go off and play.
I said no bluntly to further requests that he be allowed over to play. He invited dc3 over but then his mum cancelled 3 times in a row so dc3 never went there.
Finally she told me a couple of weeks ago (sixmonths on from the disaster playdate) all about his ASD diagnosis and how he's excluded from school while they wait for a place in a special unit with 6 children per class etc. He was diagnosed exceptionally early she told me, she has a 2 year old and said how dc1 was in the process of getting diagnosed at the same age, and how different the two children are...
The thing is I cannot get my head around why she didn't tell me before she let her child trot over alone to my house and drove off to the shops or wherever she went. If she'd forewarned me I could surely have been better prepared for managing his very difficult behaviour. I assume she was desperate for a break but I'm still that she knew what he'd behave like and didn't give me a heads up and a few tips on how to manage him
Mostly though having 5 or 6 kids in the house is easier than just my own as they amuse on another, and are no trouble. I happily left an 4 kids between 12 and 9 alone in my house for an hour at the weekend (2 were mine and the other two had been sleeping over parents were forewarned and said of course it's fine) while I took my youngest to his activity, and returned to find they'd tidied up brunch before starting the Wii bowling game I'd said they could play while I was out :o