Since I always weaned at 4 months I actually started haltering very early in their young lives. I stalled dams with their little ones at night for the first month. They stayed in their stalls with momma for the first 3 days, until true bonding had occurred, because they were much easier to handle once they knew how to listen and pivot on a dime if momma called to them.
I left momma and baby alone the first few days, and then introduced myself slowly in each stall, sitting in the hay and constantly talking to baby. Most were very inquisitive and had no fear of me, since momma wasn't paying me any attention or showed any signs of alarm, they would eventually come out from behind momma and wonder who or what I was. Then after day 3, very calmly I would lead momma and her little one to the mare/foal pasture, where they could frolic with other little ones, under the watchful eyes of momma.
By the beginning of week two, me being in the stall was a "normal", and I would then bring in a halter and introduce it. I let them get quite used to it, the smell of it, etc., and used it to help me give scratches and tickles, getting their own smell all over it. Then slowly I'd introduce it to them by putting it on and off their little heads -- just for minutes at first, giving up calmly if it scared them at first, but usually just on and off -- just like picking up their feet and putting them down, and introducing them to the brush. But it was always off when I left the stall, and had it hanging from their food dish. Yes, each baby had a food dish for nibbling, and most did.
By the beginning of week 3, I'd attach a lead rope and let them get the feel of dragging it around their stall, since that's quite a new feeling. and by the end if the week, since I had a closed in barn with an aisle, I let them out in the aisle with their new little friends, each dragging a lead rope. What fun they had. Sometimes I'd pick up the end of the lead, so they could feel the different "pressure" that caused, and then back in the stall with momma.
By the beginning of week 4, I would halter and lead rope each little one with their momma, and lead both to the pasture area for playing. Leading them with their mommas first seemed to make any leading easier, since they were quite accustomed to following close behind momma. I usually had the baby lead rope tied to momma, so they felt normal pressure from mom. I didn't allow any dragging or pulling on the halter, and we'd stop often if baby was showing any concerns or fear or unwillingness to follow.
Usually by the end of month one, they could halter and lead, have their feet picked up, and had been fully clipped -- since here in Florida it gets so hot their foal coats need to be clipped off. For that I used to put them right in my lap and clip, and they usually all fell asleep when the clippers were doing their job.
Next, of course, came leading without momma, and sometimes I did use a rope behind their bum to encourage forward motion. But, really, I seldom had any problems. Then came training to just stand which was done during dinner time with mom in the stall, and baby with his/her dish on the outside of the stall, and tied. Then I would remove the dish and have them get used to standing outside the stall with no food encouragement. As soon as any "fretting" was noticed, I would calm them down and quietly lead them into the stall where food was.
Generally, this worked for me. My niece always thought it was so cute to see an entire herd of babies tied to the barn in a row, just standing quietly as I brushed them, lifted feet, and talked to them, increasing the amount of time they were standing. By then, mommas weren't paying much attention to the process, and the babies were surrounded by friends, so there was little angst.
A couple of my mares always weaned their foals themselves before the 4th month, which was when I separated them for weaning if it wasn't done. Since they were with friends, there was little trouble and weaning always went smoothly.
We all do it a little different, so you just have to tweak things to see what works best for you.