I hauled my mare and foal in a stock with a divider. Divider locks to wall to create a big open trailer and that’s what I did. I left the mare and the foal loose and removed halters. Both of mine were easy to halter and this made me worry less. I hauled several times with no issues (had to haul for breeding and pregnancy checks). For short trips, I did not bed the trailer (stock blows dust into their eyes with bedding). For hauling to inspection I did bed the trailer heavily and they wore fly masks.
It actually gets harder when the foal is older because they loose interest in following momma onto the trailer–definitely becomes a two person job at that point. I do think the lack of ramp made it easier–we did load once onto a ramp trailer and the baby jumped the ramp on and off, which was NOT ideal. More hands to help out would have been good that day.
There is no chest bar on the trailer I use, but I agree with Callaway and would want to do something to discourage the foal from going under/over it if there was one.