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The angles were designed to make cape projects easier -- to some extent, you can follow the lines and cut. Measure your child's neck area, then angle down, enlarging the base. Patterns tend to use between 16-23."
Sew ribbons over shoulders and under the arms for an easy solution. Or sew short sleeves. If you shape it like a backward bib, remember to keep the neck area comfortable and loose.
Add a pocket for carrying things! Some cape designs use simple backpack layers underneath the shoulders.