Among one of the new features introduced in Fire Emblem: Awakening is the possibility of further developing the support relationship between characters of different sex: achieving a Support relationship of level S will make them marry and let you use their children as playable characters in your unit.
There are a total of 13 children available in the game which can be acquired in Paralogues and Side Missions, appearing after the corresponding mother gets married. Children will start joining you after Chapter 13 has been completed.
Please note that only certain marriages will give you children and the parents’ stats, skills and classes will deeply influence their abilities so make sure to take good care of all the possible parents. Not getting any of these children will not only deprive you of possible strong units in battle but it will also prevent you from accessing most of the game’s Paralogues.
There’s also no chance to miss the Paralogue mission where you’ll be able to recruit the children: after two characters have married their corresponding Paralogue chapter will appear on the world map after chapter 13. Because of this there’s no need to give any of the character the support relationship of level S before this chapter, except for Chrom, who’s going to get his first children during Chapter 13, no matter what.
Also note that both Chrom and your Avatar have the ability to have two children; all childrens will join you at level 10 and can reach a relationship level of S: however, they can only have children if married to your Avatar. Also, all children will start with a C relationship rank with both their parents.
Children will get their parents’ last equipped skill except for Chrom’s children who get the Rightful King skill. Using this feature will allow you to create some interesting combinations and create some devastating units, taking the best features of their parents.
Morgan will be your Avatar’s son: his or her sex will depend on the sex of your avatar, being the opposite of what you have chosen for your Unit. Morgan will be able to get even more classes choice depending on the wife or husband of your unit: if you pair the Avatar with a character who can change into Manakete, Taguel, Villager, and Fighter even Morgan will be able to. The only unaccessible classes will be Lord and Dancer. If the parent is Chrom, Olivia or Lucina, Morgan will join as a Tactician with the Veteran skill together with his/her inheritance.
Article from Gamersyndrome.com