osage might be too hadr to carve for thoise young ones... you could make "panda" bows- that's where you lash together a small bundle of bamboo- the pieces are selected and arranged to produce a bow with out doing any regular tillering. Don't call them "panda" bows, though, call 'em "dragon" bows or something!
another option is to use long straight saplings that are "green" - that is, not seasoned. make 'em like 6 feet long and they should be forgiving to tiller. green wood will be easier to carve. 10 year olds would have a real hard time carving seasoned osage and most kids don't want to spend a day or more making a bow- they wanna go shoot it. with the panda bow they will be shooting before too long and if it breaks there's time to make another.
how much bow making experience do you have and what tools are available?