First, why does your 6 year old brother have access to a machete?
2nd, boards will have grain violations so only pick boards with a minimal amount grain violation.(see George's site)
third, screw drivers are not bow building tools. They can be used in some applications but rarely.
Antique/thrift shops have good, old draw knives for about $20. A wood rasp, a small ax and a cheap pair of scissors(disassembled makes a great scraper) is a way to get appropriate tools for not much money. The wood rasps and small ax can be found at antique/thrift shops too.