For cortical bone, important changes of the elastic properties values have been clearly shown in ageing but not in childhood, furthermore recent works considered osteoporosis as a pediatric disease with geriatric consequences and children are concerned by specific infantile osteopathologies. That is why there is a strong interest in the characterisation of the growing process of children bone. However, few mechanical properties of cortical growing bone are available in literature and do not yield to gold standards. In this work, we have analysed surgery waste (bone transplantation) from long bone (fibula). In a first step, a non destructive method was used to evaluate the velocity of ultrasonic waves from which the acoustic Young's modulus Ea is calculated using the difference of sound path duration and the mass density. Then, in a second step, a destructive method was used to obtain mechanical Young's modulus Em using a 3-point microbending. The children samples (4 to 16 year old) show an average Ea and na of 15.5 GPa (+/- 3.4) and 0.24 (+/- 0.08) at 10 MHz , and an average Em of 9.1 GPa (+/- 3.5). Ea and na are in the same range for children and seniors but a linear correlation between Ea and Em is found only for the fourteen samples of the children group.