Measure what size you want your charm to be.  

For my shoe I decided 30mm is good, though you may want to choose something smaller for a kid shoe.  

You should also measure the width of your laces so you know what size hole to fit it through.  My laces are about 5mm but I think there is a little squish factor there so I'll make the holes 4.5mm.

Make a rectangle the size of your charm and add two circles for the laces.  I moved mine in 2mm from the edges so it's not too thin as I don't want it to snap later.  

Align the two circles together and vertically align them and then choose Group.  Now select that group and the rectangle and align it vertically and horizontally to make sure everything is centered.  

I'm not a fan of sharp edges so I'll round the corners to 2 as well.  Make sure the circles are in front and then select all and subtract to create a single piece.  Set this to cut.

Now you can see what size you have left to engrave a design or lettering.  Again, kid shoes may have less space so you'll want to factor that in.  Too small or intricate and it will be hard to paint or read the design.

I chose the word "dance" for mine.  Set it to the size you want and align it vertically and horizontally.  Set this to engrave.

Fill in your engraving with paint.  In retrospect I should have left the paper on for this step and I highly recommend that as it's easier to clean up.  

Put a tiny amount of rubbing alcohol on a paper towel and gently wipe the top.  We just want to remove extra paint from the surface but we do not want to remove from inside the letters so only use a little alcohol and pressure.  You can touch up with the paint pen or brush after you are done if you went a little overboard on either, though.

Unlace half of the shoe, slide your charm on, and relace it up. All done!  Now you are ready to go out with your new accessory.