Let's discuss this a little bit. Each chicken has its own personality and each flock has its own dynamics. We all have different circumstances, set-ups, and so many other differences that we can all get different results even if we try it the same way. Sometimes integration is so easy you wonder what all the worry was about, sometimes chickens die. Very much like NatJ said.
In my opinion how much room you have and the quality of that room has a big part to play in how successful integration is. Extra room does not give you a guarantee that you will be successful but I believe it helps a lot. By extra room I don't mean square feet per bird but can they get away and stay away from the others when they need to. You'll see us talk about clutter. That's stuff they can hide under, behind, or above to break line of sight. Clutter can improve the quality of what room you have. When I'm integrating juveniles, when I go down in the morning the juveniles are typically on the roosts while the adults are on the 8' x 12' coop floor. They can avoid the adults because the roosts are high enough the adults can't peck them from the floor. If I have a second younger group of juveniles in there they are typically hiding in a tight space under my nests, away from both older groups. That's some examples of how clutter can work.
Dad's method of integrating was to release the chicks in the area of the hen house without any "look but don't touch" and walk away. It worked for him. He had a flock of around 25 to 30 adults that totally free ranged. Most slept in a henhouse at night but several slept in trees. Most of us don't have that type of room and most of us would not accept them sleeping in trees. I would not recommend Dad's method for the vast majority of people on this forum. They are not set up for it and don't use those management methods.
I have no doubt some people are successful by putting perfect strangers in the coop at night and letting them wake up together. I don't know their details. Do they leave the pop door open so they can escape the tight coop as soon as they wake up? Do they have enough room that they can get away from the others? Do their chickens sort out the pecking order before the humans know it? Do they only do that with adults? I'd be a lot more nervous with chicks than adults.
I'm not sure how you went about it last fall. With 3 hens and 4 chicks it's very possible your room is pretty limited, both in the coop and in the run. That can make it harder. It's easier for me to make specific suggestions if I know what you are working with. In the Bay area of California you should have reasonable weather pretty soon. How big, in feet, is your coop? How big, in feet, is your run? Photos of what the coop looks like inside and how the coop and run go together could be valuable.
Without that information all I can do is what the others are pretty much doing. Give you generic suggestions and let you work out the details. House them across wire for a while so they get used to each other. When you let them merge give them as much room as you can and use clutter to improve the quality of what room you do have. Provide at least two feed and water stations well apart, preferably put of line of sight of each other. Try to not force them to share a tight space if you can avoid it at all. Try to let them work it out at their pace. Don't believe they have to sleep on the roosts next to each other. I don't care where mine sleep as long as it is not in the nests and is somewhere predator proof. They'll work that stuff out later. If there is enough size difference the safe haven concept my help. That's where you provide openings the chicks can get through but the adults can't so the chicks can escape to a safe place if they need to. When you first let them mingle at night, be down there at first light as they wake up to see how it is going and so you can open the pop door and they can escape.
People successfully integrate all of the time, even in tight spaces. You can manage but sometimes are easier than others.
