Ligament laxity tends to run in families. It is due to the connective tissue that makes up the ligaments having a little more give in it than the average person (having said that it is very common). Hypermobility can lead to difficulties with gross and fine motor skills in children and to some joint pain with instability in adults. You can't do anything to tighten up the ligaments in anyway, but you can exercise the surrouding muscles to help stabilise the joints. See a Physiotherapist for a full assessment and an appropriate exercise programme.