I was asked for some tips on how to help children sew straight seams. First, you need to realize that children don't have the same coordination as adults. They also learn differently than adults. They will need a lot more practice and repetition.
The most important tip I can give is to have patience and don't be too critical of their work. In class we only seam rip if the crooked seam actually impedes the use or finishing of the item.
That being said, my favorite tool is the magnetic seam guide. They come in a variety of shapes an sizes and can be found at any fabric store.
This handy little tool "sticks" right to the metal on the throat plate on your machine.
It provides a large edge to help guide the fabric. You will easily see that the fabric is creeping too far off the seam line
Important tip if you have the guide with the knob on the top
Please teach your children to place this style guide on their machines with the knob facing their stomachs and in front of the needle screw bar. On some machines the needle screw bar will hit the knob and it will bend your machine part.
If your machine has a large plastic area around the throat plate you should look for the long magnetic guide with the knob. This longer style will reach to "stick" to the screws on the throat plate. The shorter style will not have enough room to grip and will keep sliding towards the metal screws.
Another helpful tip is to sew puzzle sheets. In class we like to do a sewing warm up exercise before starting on our projects. I have the children sew dot-to-dot and maze puzzles without thread in the machines.
Sewing puzzles is a fun way to help them practice visual coordination and speed control. It reinforces sinking the needle before turning a corner and they can visually see how tight they are holding their projects. If you are pushing or pulling the paper it will tear. If you are stitching correctly the puncture dots will be nice and even.
I hope these tips help. Happy Stitching!!