J.C.
Oh, dear - yes, boys are surely different ( and in their teen years they are often sweeter and easier for Moms' to deal with than girls are--- I said often--- no guarantees)
1. Boys are WAY slower to learn to control their impulses
2. Boys need WAY more physical intervention ( I mean you may want to pick him up and remove him from the area -I'm not suggesting you strike him) --
3. Boys need you to be even more consistant than you needed to be with girls--- so EVERY single time he hits you ssay '''' you hit-- you sit'' and then you pick him up and put him in the naughty spot-- or even take him out of the room and put a baby gate up--- Boys learn really well from our body language---less well from our words -- so your body says ( by picking him up and removing him from the ''victim'' - '''no- you can't do that'' -- your words won't get the message across---but what you DO -- will.
Blessings, dear heart-- it makes perfect sense to me that a 19 month old boy finds a 4 year old and a 6 year old sister frustrating and looses it- they TALK and use their language skills SO well - that he may feel completely left out- so he tries to get ''back in charge'' by being physical-- it needs to not work for him.
Take care of YOU -- you have a delighteful and difficult task-- you'll do it - -I guarantee it. ( any chance you could put him in a one-day-a week co-op preschool where he could be around more babies his age???
Blessings,
J. - aka- Old Mom