How many payments did you miss? If they are calling in the whole debt, you need to be honest with yourself first. My guess is it is more than a couple of payments. If you really cannot pay this, your best bet is going to a debt management company like CCSS who will negotiate with the coop on your behalf and get reduced payments (and even some of the debt written off).

They cannot levy goods belonging to children. This is unlawful. You need to write a letter (fax it and mail special delivery to the bailiff firm and copy in the council) explaining that you are aware they are acting unlawfully in threatening to do this. In that letter, make it clear that bailiffs will not gain access to your property under any circumstances. Once you have faxed it to the bailiff company, phone them and make sure they have received it. On the phone (and in the letter); ask which court the bailiff got his certificate from and explain that you intend to complain to the court about his behaviour. (There's a link on this forum somewhere to a form you can use to do this).

Re the council refusing payment and telling you to go back to the bailiff. I paid my council tax on their online system; then wrote them a letter, including the printed copy of the receipt and copying in the bailiff. I made it clear that this was the OUTSTANDING amount owed, NOT going towards this year's council tax. They accepted it - how could they not? The bailiff was then informed.