toddler behavior

I have 3 daughters, 2, 4 and 10. The 2yr. old is constantly picking on the 4yr. old and making her cry. When my 2yr. old gets mad she pushes and hits my 4 yr. old.  My 4yr. is thin and frail and my 2yr. old is chunky and strong, so it hurts her when her little sister hits her.  I've told my 2yr old not to do that.  It seems she doesn't listen, but she keeps doing it.  I tell my 4yr. old daughter she needs to defend herself and get mad and say "no, don't hit me" to her sister, if not she's always going to get picked on by her little sister.  Sometimes I wonder if this is normal behavior for a 2yr. old.  She has a very short attention span, It seems that when I sit her down to talk to her, she's not really understanding what i'm saying and she just wants to get up and go play.  When i say "don't do that" she just keeps on doing it, doesn't really listen to me. She likes to play very rough and when I give her a hug she smiles and tries to hit my face or poke my eye and i serioiusly say "no!" to her so she can stop. She's a very hyper child.  What can I do so the fighting between my two little ones can stop?

[babygirl6152]

time outs work- at this age- don't be scared that she won't understand- she very soon WILL/

it's just that the training takes a while- but you can't tolerate any of it- put her in time out every time- be consistent- and I am glad your other little girl is learning assertiveness- it was worth a try- but it didn't work so you have to guide little 2 year old til you are sure she can understand- and I know it's hard to know at age 2 but she will "start to understand" very soon if you work with her- should take awhile and she may even get worse at first-