Mars-born children
Adult settlers will start colonization, but eventually children will be born on , the next generation of a growing of Mars colonists. Either the progeny kid carrier of the first settlers continue the colonization process or, to avoid , embryos with a maximum of genetic diversity are brought up (inspired by ').
Effects of gravity on growth
Experiments in zero gravity show that animal embryos do not develop properly in zero-g. Mars has 0.38 gravity, so, even if the said child was not deformed, that child would develop and grow in 0.38 gravity. So, the child may be extremely healthy by Mars standards, but severely weak by Earth standards.
Immune systems
Children growing up on Mars will not come in to contact with microbes as Earth children would. Thus, it is important to vaccinate them to boost their immune systems.