Duplo compatible railing/fence generator in OpenScad. You can easily tweak any parameter you want. Turn on or off middle cross-section or Y offset. Make it extra long, short or high or without vertical planks.

Original Duplo brick reference on Bricklink:
Brick ID 12602

I recommend to print with tree supports and 100% infill as it's quite fragile.

It might be needed to tweak these two variables depending on your printer/material/extruder
duploStudUnit - basic horizontal stud offset
bottomInnerFrictionFitDiameter - bottom stud connector inner diameter to fit on top of normal studs