Hello Hopemore. Happy to answer your questions, though you may find answers to these and more questions http://anglicansonline.org/basics/expect.html on this website, which is American (I think) but covers most of the basics of Anglican worship wherever you are.
In answer to your specific questions:
It's customary to stand for certain parts of the service and to sit (and sometimes kneel) for others. In some churches you may also move in your seat (e.g. in my church the gospel is read from the middle of the central aisle rather than from a pulpit or lectern, and the congregation turns to face the place from where it's being read). However, if it's difficult to stand then it's fine to sit. If you stay seated, I imagine most people will assume it's because you find it difficult to stand (whatever the real reason is), not that you are being somehow rude and defiant.
It's not rude not to put money in the collection. People should give whatever feels right to them and what they can afford. There are all sorts of debates about this, but there is no single 'correct' answer. I sometimes take up the collection, and if people don't reach into their pockets when they see me coming then I just keep going - I'd rather miss someone who intended to give (they can always put money in later if they want to) than stand next to someone who doesn't want to or can't afford to making them feel uneasy about it. Anyway, some people give by Direct Debit, so there's no way of knowing from who puts what in the plate who is actually giving and who isn't.
Why do people go and have bread and wine would require a longer answer than I have time for. The simple answer is that they do it because Jesus told his followers to do it in remembrance of him. What the bread and wine are or represent may vary depending on the different denomination, church or individual, but basically there is always the sense of fulfilling a direct instruction from Jesus before his death on the Cross.
Who can take communion also varies depending on the individual church. Some will say any baptised Christian of any denomination, some require you to have been confirmed into the Anglican Communion, and others have a halfway house scenario with a special service of admittance to Holy Communion. You should see what it says in your service booklet if you have one (ours is very clear on who can take communion and what to do if you prefer just to receive a blessing), or, if it's not clear, ask the vicar.
If you don't want to share wine from a chalice that others have been drinking from (or, indeed, if you have a nasty cold which you don't want to share with all and sundry) it's fine to dip the bread in the wine rather than to drink from the chalice. (NB this works better if you're in a church that uses communion wafers rather than 'real bread' - with real bread there's a danger of disintegration and a crumbs-in-the-chalice situation.)
Finally, the no Sunday Church for Children on the first Sunday of the month will be a local arrangement and you could ask the vicar of the person who organises Children's Church. It may be that once a month they have an 'all age' service, with the children in the main service rather than out at Sunday School or Junior Church or whatever they call it... But it's impossible to know exactly - you will need to ask on that one.
Please don't ever feel afraid to ask. No-one will mind - you don't have to show up already knowing all the answers. Just to whatever you feel comfortable with and enjoy.
HTH and best wishes