Your heart sings when your child is mobbed by her classmates, and breaks when they run off for a quick and forbidden clamber up the grass mound; inaccessible to your child in her wheelchair. It's a great leveller.
You get to pair up parents to children, spot who belongs to who, have a brief chat or just exchange sympathetic glances; the instant understanding you can only gain when you too have been the parent of the child screaming loudly in the buggy or smearing secondhand peanut butter all down your jeans. And, you get to just ask, casually, "would little Jimmy like to come to play one day?" and just like that, it's all sorted out.
When your child rides the bus to school, you lose all that. You lose reading the notes the PTA post on the noticeboard in the playground. You lose reading the poster declaring what colour, what letter, what shape this week is going to take in your child's class. And you lose the connection to other parents. And when your child is the only child in the school to be riding the school bus, the school is not set up to provide other ways of picking up on this information.
So, when your child comes home saying "Can Fifi come to play?" you can't just collar Fifi's mother the following morning. You have to write a formal note to Fifi's Mum, not knowing if Fifi's Mum usually brings her to school or if she comes with a childminder. And you can't just offer to pick both girls up from school, because of course your child rides the bus, and the bus has no space for friends. So you have to suggest a weekend or day off. And, because you don't know Fifi's Mum, you don't know if she has picked up on your own child's special needs or not - and, because you don't watch your child on her way into school you don't know if Fifi is really her friend or just someone your daughter really wants to have as a friend but who is actually quite horrible. And you have to rely on school passing on the note, and then you have to hope Fifi's Mum is nice enough that she will reply to it and not think it odd that you've written to her rather than just collaring her at the school gates.
Happily, Fifi's Mum was in fact a very nice and understanding Mum, and Fifi was in fact a very nice and happy girl, and even more happily, both girls saw each other on Sunday and grinned and giggled and fizzed at each other.
And so, in ninety minutes, two girls played with the toy kitchen, explored the bedroom, explored the garden, played the piano and the guitar, bounced into the ball pool and back out again, found the dolls and the dolls' house and the buggies, iced some raspberry buns, ate some raspberry buns and rather more icing, raided the fruit bowl for apples, rejected the drinks, settled to some colouring, found some dressing up, bossed each other around, cooked another menu at their pretend cafe, and found some more dolls to dress and style their hair.
And even more thankfully, Fifi's Mum turned up and took Fifi away again, and both girls parted company reluctantly but happily, and with the faint hint of a suggestion that Little Fish should go and play with them one day.
And then it was bedtime, and I think I've been recovering ever since!