Snack bag instructions (pic heavy)...

Cut two pieces of fabric approx 30cm x 18cm - I used a cotton outer and nylon lining (apparently food safe)

Pin velcro (approx 15cm) as in pic

Carefully stitch close to the edge - I use stitch width 0 and length 2

Pin right sides together (ie the velcro will stick together).  Stitch down each side leaving about a 3cm gap on one side (you'll need this to turn the bag right side out later)

Turn lining right side out and set aside

Pin outer right sides together

Stitch the length of each side - I use stitch width 2.5, length 2 and use the 1/4" guide

 Place the lining (right side out) inside the outer

Pin together making sure seams are aligned nicely

I suggest if the arm of your sewing machine is a bit wide to make the snack bag a little bit wider - it was a really tight squeeze on mine.  Stitch all the way round.

Your work should look like this so far

Turn right side out by pushing through the gap you left in the lining

Stitch the opening closed - I used stitch width 0, length 2 but you could also hand stitch this closed

Push the lining into the outer and you're done.  For children's snack bags I recommend stitching a seam along the top just to reinforce.

 Hopefully these instructions are clear enough.  I recommend researching the fabric you intend to use to make sure it is food safe first.  Alot of fabrics like oil cloth, PEVA and PUL are not food safe.