When do you know for sure - Right/Left handed?

[Claire2009]

DD is 3.8yo, I'm pretty sure she's right handed, DS is 2.6yo and again, I'm pretty sure he's left handed. Is left handed-ness from genes or just random? I'm right handed and ex is right handed, I don't know anyone left handed?

He draws/eats/picks things up with his left, kicks with his left.

ds could be left handed but it's still too early to be definite I think. my dh is left handed, as his his mother and brother, I'm right handed and our dcs are all rigth handed but they all used both hands for things until they were about 3yrs old and ds1 would switch between hands when using a spoon for cereal in the morning for example even at age 3 but he would use his right hand for holding a crayon.
even though he's lefthanded, there are a lot of things dh does that we right handed members of the family do - the way he holds a camera, plays the guitar right handed (interestingly ds1 plays his as if lefthanded!).

DD was definitely left handed by the time she was 2. She had ot have her hand bandaged for a few weeks when she was 2.4 and she managed right handed ok but went straight back to left as soon as the banadaged came off.
DH and DS are right handed, I am a mixture ie write with my right but do a lot of other things that usually involve strength with my left ie opening bottles and lifting pans.

There are quite a few left handers in my side of the family.

I wasn't sure about DS until he started school - he is right handed.

DD also right handed but I was sure about her from when she was about 2.