Question: Is there something to worry about when a two-year-old is spending most of her playtime at daycare crossing her legs in every possible position trying to get her diaper to give her a pleasurable sensation, and on the other hand attacking all the other children without any reason, and without showing any emotion either, she never laughs unless you tell her to, thank you for your helpAnswer: I'm not an expert on childhood behavior so I am not sure I can be of much help or if what I say is true.
I am aware that young girls do at times spend a lot of time masturbating and may not be the least bit shy about it. It simply feels good to them. If you interrupt them, they may get mad and show their displeasure. You can read one mother's experiences at the link given below.
http://archive.salon.com/sex/feature/2001/05/23/like_mom/
You do want to periodically examine a young girl's vulva when you bathe her, or change her diaper. Look for signs of irritation like diaper rash, fused inner labia, and hardened smegma under the hood of her clitoris. An unpleasant odor or discharge could indicate an infection. Reddish warm labia and clear/whitish liquid that comes and goes could indicate sexual arousal and should not be a reason for concern. Sexual abuse might be indicated by injuries to the vulva, like a torn hymen.
It may be wise to at times leave her diaper off so she can explore her body freely and perhaps have an easier time at masturbating, perhaps at bed or bath time. You can lay her on one of those plastic lined bed pads they sell for incontinence and cover her with a sheet or blanket. You can also shower or bathe with her and give her time to explore; she is too young to bathe alone. I would recommend that you be as tolerant and supportive of her self-exploration and masturbation as your individual circumstances permit.
The striking out could indicate she does not know how to interact with other children, if she is an only child and does not play with other children at home. She may simply want attention and wants people to notice her, which they likely do when she hits another child. If this is the case, she should be included in group activities and receive more adult attention. You want to keep her from hitting versus reacting when she does. It could also possibly indicate emotional discomfort and frustration. If the people around her are not happy, she may pick up on this and be reacting to it. If her parents and caregivers are not happy, neither will she.
The fact that she does not laugh is a bit disconcerting. Does she laugh when she is tickled? Does she smile? Does her face light up? It may indicate someone needs to take the time to figure out what makes her happy. Perhaps someone needs to spend more time holding and playing with her.
Something that may help with all of this is infant massage. Undress her and gently apply body lotion to her entire body. Use light caresses. Massage her hands, fingers, feet, toes, face, etc. The same techniques that apply to adults can be used, but there are also books available on infant massage. This will help with any stress she may be under and make her more at ease with her body. If she wants more attention this will provide it. Bathing and sleeping with her parents might be wise as well.