The spirits Seth created using magic to protect the baby have both Seth and Theo's energy (they did create them together). So he called little tiny Theo "Theo's spirit". When I read it in Spanish they more clearly imply that the spirits reflect who they are, really. So, Theo's little spirit is more shy and meek, contrary to how Seth thought Theo was. And little Seth is very protective of Theo. Agrish's lover tells him that Seth is fearful, not because he real Seth demonstrates it, but because his little spirit version does.
Ohh right they did breathed on those leaves. I actually thought the spirits will be the kid's spirits.
How? How did the little theo became theo's spirit?? Kinda dont get it