I used a trailer with our son when he was very young, and actually felt it was safer than other options. With a child trailer I found that cars give you a wider berth. It's lower to the ground, so no concerns of the kid dropping any distance and hitting his head. The trailer is only a foot behind your bike. A car that hits a trailer you're towing is going to hit your rear wheel and wipe you out on your bakfiet too, so not sure if there's any real safety benefit there. The trailer that we had, I could actually roll it upside down and our son would stay in the middle safely strapped into the seat (just upside down), so there was actually a fair amount of protection.
One thing I found though, was that when my son was very young putting a helmet on his head was causing a lot of problems. The helmet was too heavy, and then when we went over bumps his head bounced up and down too much and he didn't like that. By the time he was two this stopped being so much of a problem, but before that I had to strap a car kid's seat inside of the trailer and forgo the helmet. YMMV though.