Mars-born children

Adult settlers will start colonization, but eventually children will be born on Mars, the next generation of a growing population of Mars colonists. Either the progeny of the first settlers continue the colonization process or, to avoid inbreeding depression, embryos with a maximum of genetic diversity are brought up (inspired by The Cascade).

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 severly 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 import to vaccinate them to boost their immune systems.