Now - before I am considered to be leaving out half the population......naturally these projects are perfectly suitable for girls too!!!!
My daughter has never really been interested in sewing. In fact I cant remember her making anything this way although she is very creative in other areas. No

wait- she did make something for a school project once- with a lot of help and complaining lol.
However about 6 months ago my two boys (aged 6 and 8 ) watched me sewing (on the machine) and eagerly asked if they could 'have a go'.
I was impressed by this unexpected interest and so as soon as id finished what I was sewing up I sat them down to start a little project of their own.
I figured it had to be very simple and quick and easy.
PROJECT ONE (A BAG)
So i had them mark out a rectangle shape on some fairly stiff material (so it didnt move around too much) using a cereal box as a template.
Then they cut it out (with a bit of help for the youngest.) and folded it in half.
Next they took it in turns to sew up the side seams (so they had a bag shape.)
Then we found two nice big shoe laces ( we happened to have a packet in the drawer - but you could steal them out of DH's runners, haha)
Finally I helped them to fold over the top of their bag (leaving a generous seam) and sew around creating a 'pocket' all around the top into which we pushed the shoelace. (thats why we used shoe laces- the plastic tip makes it easy to push in - also we had a nice wide seam so it was not a struggle to thread the lace through.
Voila- a draw string bag.
They were SO proud of their efforts and couldnt believe they had actually made something!!!!!!!
PROJECT TWO (A Mouse)
Our next project (next time they asked- a couple of months ago,) was for them to make a soft toy each,
For this they had to cut out a circle each. ( a big dinner plate works)
We happened to have some fur fabric.
fold it in half (right side IN )
Then they slowly and carefully (with me operating the pedal btw) sewed around the semi circle shape - leaving the end open.
They then stuffed the shape. (we actually raided a cushion in the lounge - shhhhhhh dont tell anyone ROFL)
I sewed up the open hole for the younger one but the older one carefully sewed up his own. - just before you close the end insert a shoelace (this is the tail.)
Next they had to cut out TWO circles of pink felt (using a cup as a template.)
Around one circle do a running stitch (so you can pull it in to form a ball with an opening (i hope that is understandable) sort of like a tiny drawstring bag-
The other circle is cut in half to form two semi circles,
The ball shape is the nose- The semi crcles are ear - if you curl the points towards each other a little they make a reasonable ear shape.
We just hot glue gunned the nose on and I sewed on the ears cos they are a little tricky.
The boys then used a marker pen to draw in the eyes.
Voila- a mouse (or a rat or a possum- whatever they prefer!)
I will have to go and take a pic of these so it is clearer what they look like- I found it rather hard to describe!
Hope this inspires you to try out simple sewing with your kids (boys and girls ;-)
Enjoy!