4yr old with teenage attitude- just a phase?

[Supercherry]

Hi, I'm posting this on behalf of my sister. My usually adorable and sweet natured nephew, 4yrs, has suddenly started to develop some serious teenage attitude. He won't co-operate with getting dressed in the morning, kicking and running off, no amount of bribery or persuasion seems to work. My sister has to resort to physically grappling with him to get his clothes on or else she wouldn't get out of the house. He has started shouting 'I hate you' when he is annoyed. He seems quite angry sometimes.

He is normally very nice with my DS, 13mths, but last night while playing with DSs toys started to push DS away when he tried to join in. He is gently reprimanded. It ended in my nephew saying DS wasn't his cousin anymore, he hated him and storming out of the room.

Is this just normal for his age or do you think there might be something troubling him? How do we deal with it? I'm not a big fan of strong discipline, and to be honest, he has had to deal with his parents splitting up 18mths ago- listening to rowing. His dad lets him down when he is supposed to be seeing him. His dad has just had a baby with his partner.

My dd is almost 5 (but sometimes thinks she's 15). We're expecting a new baby and for months now she has been extra affectionate (I love you mummy, I'm going to live with you forever, etc.), however this is occasionally tempered by the odd bought of stroppiness/rage:
yesterday when trying to wash her hair, she spent the whole time screaming/shouting (I hate you, I hate you), hitting, pushing, trying to bite me, etc.
I think this is because i. generally unsettled because she knows new baby is coming and ii. specific case of hair washing, doesn't want it done and wants to stop me.
I just try and rise above it, saying 'I love you' when she says 'I hate you', and trying to distract, give cuddles, etc. Was like this but more frequent when she was a toddler, so same principles apply I think. (obviously these tactics are easier if you're not feeling tired/irritable yourself!).

I wouldn't say it had anything to do with teenage attitude!
He is a very little boy and a lot has gone wrong in his short life. His father leaving him and 'replacing' him (in his eyes)will have had an enormous impact, plus the fact that the father can't be handling it very well if he keeps letting him down. If his new partner isn't treating him as her DC and the older brother and equal to his baby sibling it will be very difficult for him. It all seems a very new relationship so I would doubt if the father and partner are putting him first. Added to that he had all the rows when he was younger and I dare say his mother has found it all very emotional and isn't at her best.
I would say that he is a very angry, little boy-his world has been turned upside down and so it is no wonder he isn't adorable and sweet natured.
Strong discipline isn't the answer. He need to feel very secure and that his mother, at least, puts him first. I think she needs to do a lot with him, give him masses of attention when good and distract or ignore when his behaviour is poor. Try and make the getting dressed etc a game.

Thanks for replying, it's hard to know if it's just a normal 4 yr old phase or if he is responding to the circumstances that's why I posted really. I do feel really sad for him happyflower, I didn't mean literally teenage attitude, just that it's a way of describing the type of behaviour. I was also thinking along the lines of just ignoring naughty behaviour and going easy on him. I would say my DS is more like a brother to him than a cousin they are so close and I have always treated them equally if that makes sense. I give my nephew lots of attention and praise and say how he is my DSs favourite person and how much DS loves him (he really does). However, I think my sister finds it difficult to ignore being kicked in the face when trying to dress him. You can't really ignore it when he won't get dressed- she has tried games etc but nothing seems to work.

My sister is in a new relationship now and they are happy I think but she still does pretty much all the childcare on her own so she is probably frazzled.

Perfectly normal behaviour. Has she got a copy of 'How To Talk so Children Will Listen?' It has some really good strategies.

I will have a look on Amazon- thanks Cornsilk.