Adjustable bag straps are the best! Not all patterns have adjustable straps though (like Horrible Harry's Pirate Backpack Pattern). Here is a quick and easy tutorial on how to make adjustable straps for a kid's backpack. You can also use the same technique for handbags, tote bags etc.
Make the straps as per the pattern instructions. This particular pattern has straps that are 70cm (28") long with a finished sewn width of 2.5cm (1"). To make the adjustable straps you will require some hardware, we have used 4 x 25mm (1") Slide Adjusters.
Step 1: Bottom Ring Strap - Cut off an 8-10cm (3-4") piece from the end of each strap. Fold each piece in half around one side of each slide adjuster to form a loop.
Sew horizontally across the strap as close as possible to the slide adjuster. This keeps the slide in place and stops them from twisting around.
Step 2: Adjustable Strap - Take a long strap and zigzag across one of the short ends to help stop the fabric from fraying. Thread the strap through the slide adjuster (under the outer part, over the inner bar & back out under the outer part).
Tuck approximately 3cm (1.25 in) back towards the main part of the strap to make a loop over the inner bar of the slide adjuster. The shortest length of strap should be on the bottom and the right side of the slide adjuster should be facing up.
Sew a rectangle shape (instead of just straight across) when joining to make the strap sturdier. Repeat for the other long strap piece.
You should now have two short Bottom Ring Straps and two long Adjustable Straps.
Step 3: Attaching the Bottom Ring Straps - Sew the bottom ring straps into the base of your backpack. The right sides of the slide adjusters should face outwards when the straps are pushed upwards.
Step 4: Attaching the Adjustable Straps - Place the bag down on its back and fold the Bottom Ring Strap downwards away from the bag. Place the wrong side of the Adjustable Strap up, so you can see the zig zagged edge. Thread the Adjustable Strap through the Bottom Ring.
Loop the strap back up and thread through the Slide Adjuster (under the outer ring, over the inner bar, under the outer ring). The zig zagged edge will now be covered. Pull through until the Slide Adjuster is about 10 cm away from the Bottom Ring.
Sew the top of the adjustable straps to the top of the backpack per the regular pattern instructions.