A while ago I had a situation where I asked my BF who was not used to kids to look after my two girls while I went to the dentist.  My blog on the situation is here.  He was very reluctant to do so, but

Anyway, in order to raise his comfort level, I wrote him a book with a series of instructions on what to do with the kids.  I thought these instructions might also be useful for someone else who either wanted to write a similar book or who is themselves a reluctant babysitter.  I wrote it in an ordinary exercise book with each heading on a separate page for easy reference.  The idea was to cover most of the situations he might find himself in when looking after the kids for a couple of hours and to impart some of the knowledge of my kids that I take for granted.

IF THEY CRY...
The first thing to remember is that kids are emotional.  They don't hide their emotions but they also get over things very quickly.  If they cry, give them a hug.  And hold them until either the crying starts to slow down or until they let go.  If they are crying because they've hurt themselves, first comfort them, then check out what they've done.  Ask them where it hurts or what happened.  You may need to ask a few times to get a coherent answer.  If there's an injury, then just use basic first aid as you would for an adult.

IF THEY'RE HUNGRY...
Easy one!  Give them food!  However, sometimes they won't recognise they're hungry and they'll just start getting ratty instead.  If that happens suggest it might be time for lunch.  I will pack:  Sandwiches, Sultanas, Apricot & Strawberry bars, Muesli bars, Bottles of water.  IF they want something I don't have, tell them "Sorry that's all we have today".  They might whinge a bit, but if you're consistent they'll settle down and accept it.

IF THEY NEED TO GO TO THE TOILET...
Take them both to the toilet.  Don't let them go on their own.  You can take them into the boys toilet if there's no child one available.  Make sure its reasonably clean before they sit down.  You may need to pick G up.  Remind them to wipe their bottom, flush the toilet and wash their hands.  But you don't need to do those things for them.  Again, you may have to lift G up to wash her hands.  You may need to get her soap, but let her try for herself first.  She'll be happier to accept your help if she's already tried first.

IF G WETS HER PANTS...
Don't worry about it - accidents happen.  There are spare pairs of undies and pants in the main part of the bag.  Take off the wet things and check nothing else is wet or soiled.  Put the dirty things in a little orange bag from the front pocket.  They're scented so they cover any smells.  Tie the bag up and put in the main part of the bag.  Put the clean clothes on G.  Wash hands.  Easy!

IF THEY START TO FIGHT...
Try to distract them from each other (e.g. offer toys, a chance to go on a slide if one is available, come and look at a book).  If necessary, take one of them away (and probably give them a cuddle).  Encourage them to say "I'm sorry" for whatever it was that caused the fight. Encourage the recipient to say "I forgive you".  (They'll often do this without prompting, but no guarantees).  If there are injuries, treat them with basic first aid.

IF THEY INJURE THEMSELVES...
Remember first up that it's not your fault.  If there's blood, press on it with a clean tissue or something similar to stop the bleeding.  Wash the wound in the sink if possible.  Put a bandaid on (in the front pocket of the bag).  If its just sore, a wet washer on the injured part can help.  There is a damp washer in a ziplock bag in the front pocket.  If it's a little one (they'll just tell you it's sore and won't cry) offering to kiss it or rub it might help.  Especially works well with G.  Just reassuring them is the main part.  If it's serious enough to need an ambulance, I have health insurance cover.

IF THEY ASK QUESTIONS...
Tell them the truth.  Try not to make it sound scary and use simple language.  But don't make up stories (unless they ask you to!).  Also don't make any threats you couldn't carry through:
OKAY: "You won't be allowed to read that book for one minute", "You'll have to go to your room when you get home."
NOT OKAY: "I'll belt you", "The bogeyman will come and get you."

IF THEY'RE PLAYING ON EQUIPMENT...
Watch them.  What you're looking for:
 - They don't get lost
 - They don't get abducted
 - They don't injure themselves
 - They don't injure other people
 - They play fair and let other kids have turns
If they take off their shoes and / or socks (some playgrounds require this), keep hold of their shoes etc., so they don't get lost or stolen.  When they finish, make sure you help them put their socks and shoes back on.

IF THEY WON'T DO WHAT YOU ASK...
First, try to reason with them.  If you explain why you want them to do something, they'll often comply.  You may need to keep reminding them though.  If they still won't do it, I usually tell them the consequences.  Sometimes these are obvious, sometimes you have to make them up.
OBVIOUS: "If you don't come and eat your lunch, you'll feel hungry later."
MADE UP: "If you don't come and sit down for lunch, you won't be allowed to have an ice cream later on."
Making them up can take some imagination!  But can be very effective.  Whatever the consequences are, carry them through.  You don't need to be angry  or firm particularly.  Just state the facts (i.e. consequences) then carry them through.