Another great way I have used is to have a great time potato printing. I have used lining paper, cartridge paper, backs of old no longer needed wallpaper , Then making sure the children are wearing something that doesnt matter, so that you dont have to keep telling them to mind the clothes. The careful bit is choosing what knives can be safely used and other things that can help to make patterns in to the potato, making sure that the tools are used carefully and they learn to put them back to the same place so that they dont get frustrated by losing things. Show them a very simple design, and possibly two different ones on each half of the potato. If you put them into two different colours , you can then show them how you could use alternate designs, or over printing things . Then it is their chance to do their own thing, and I suggest that you dont give them any ideas of what to do. Let them work it out for themselves, unless you feel they are totally stuck. Most children love the freedom to just do what they want,and then rapidly get into inventing their own patterns etc.
Another simple thing to do is to get an oblong or square piece of stiffish paper, fold in half , or into quarters, and then using scissors cutting small shapes along the fold. Open the paper up and you will have a paper pattern. This can then be put over another piece of paper and usually I will weigh the edges with such things as a pepper pot or whatever to stop it shifting. Then they can enjoy colouring in all or some of the designs and seeing what results they get. This can be repeated over a bigger sheet of paper and the pattern moved across in a regular fashion or changed angles over the page, so the child will produce their own "wallpaper" . Just keeping bits of useful paper for whenever it might be needed is good, to have a store ready for rainy days. Other fun can be had by using those annoying junk mail stuff pushed through your letterbox, Watching the children attacking it is quite cheering I find! However you need to keep it in a designated box or holder, so that children dont start picking up the post and cutting it up indiscriminately.
You can also use the junk mail to show how you can make a simple jigsaw from any picture. For the basic information, just get something rubbish that has any sort of picture on it. Then show the children how you can make a simple jigsaw by cutting the picture up into 4 pieces . Then look and see how it has turned out, and talk about perhaps better shapes you could have made. Then give each child a different pictured piece of junk mail for them to try to make their own jigsaw. Take all the pieces together and mix them up and then put the pile in the middle of the table and ask them to find their pieces and remake their own jigsaw from the pile. Some children find it rather boring, but others get quite keen on learning how to do it , and with several similar photos I was able to let one child eventually make a jigsaw from a picture of I think it was a great granny. She became very interested in the idea of making her own one off jigsaws, and thought it was quite special to have her relative on a jigsaw. Maybe you have a couple of old photos that you would be happy for the children to use, or these days no doubt you could recopy the photo onto your phone and then print some copies out to use. I think collecting things together into an "art" box similarto having a dressing up box, is a good idea. As you see a possibity in some item you add it to the box,and when children visit you it is something worth delving into. You could add squares of gummed paper of different colours , a la Matisse, for them to cut and stick onto other paper. Have a basic range but then as you find out what is popular get more of those colours. If you have a proper art shop you can visit,you may find out other things that are often cheaper and of better quality than a general shop like Works. Have you thought about scraper board? I think this would need to be for a slightly older child but it is another thing to add to your ideas for the future. Later on they might watch a bit of portrait artist or landscape artist of the week or whatever and by that stage you have yet another thing to do, So you choose your favourite seat, and announce that you will become their sitter for the morning. Quite a ruse to let you have a rest and listen to some music or read your book whilst they try to paint or draw your likeness . When you or they have had enough get them to put their names and ages on the back, and tell them to keep them to remind them of the day etc. If they are frustrated,annoyed or pleased with their efforts, you can still encourage them to have another go in the future and see what the difference is. That is going a bit further from your needs now but worth thinking of. Keep a couple of cheap pads with some well sharpened crayons, a rubber and a sharpener in the glove compartment of your car. When you go out for a picnic or to visit a garden or whatever, if they get bored they could make their own picture up, or if not you might enjoy making a quick sketch of the children yourself, to remind you of that occasion. The aim is no pressure, just enjoy what you do. Happy days.