12 month old temperment

[ljn8889]

my little one  will scream unless he is being held or has my full attention.  I do have to put him in a high chair while I am fixing meals or in a playpen when I want to do activities with my 2 & 4 year old.  I am afraid he will get into something while my eyes are not on him.  He also screams at bedtimes.  I have let him scream it out for 30 mins. and when I go to get him, he stops.  At night he drops off but for naps he won't sleep and then is so tired at night. Is this normal

[margypops]

Great advice from Angel thats it in a nutshell.. definatly best is a routine, he will get used to it...

[Angelinthemorning]

It does sound pretty normal.  Around 9 months of age they start getting clingy.  Some, like my dd and yours are very, very clingy.  My suggestions...don't immediately go grab him when he's playing and starts crying (unless he's hurt).  Just use a soothing voice and tell him you're right here in the kitchen and will be there in a minute.  
At night if he stops screaming the minute you go in there.  He's just "manipulating" you.  Let him cry it out.  If there is nothing wrong (dirty diaper, sickness) there's no reason he can't cry, it doesn't hurt them.  I've heard of some babies lasting 3 hours.  It really just depends on how stubborn he is.  (Mine dd lasted 1 1/2 the first "cry it out" night.  But, we only had to do it once.)  
I found the best thing is routine.  You need to lay him down for naps at about the same time everyday.  I know it's hard with the other two kids, trying to get a relaxing environment.  But, if you have to stick in a movie and just focus on "relaxing" with the baby to get him to sleep.  He absolutely needs to be napping.  So just find a routine that works and stick with it.  It may take a couple of days for him to get in the groove of it but, it will work.  

Also, you need to at least baby proof one room.  He needs to be able to get out and move around.  Hanging out in a playpen or highchair, isn't much fun.  Pick a room and go through and baby proof it, then just use baby gates to block off that area.  This will be better for him, b/c he'll have fun exploring and he'll start to learn to play some by himself.

Hope something in here helped.  Best of luck...