A baby's first Halloween is mostly for the adults, and that is fine. The goal is a few lovely photos and a baby who stays warm, comfortable, and on schedule.
Choose a costume shaped like normal clothes
Zip or popper-front onesies, hooded suits, and simple wrap tops work because they go on the way everyday clothes do. Anything that pulls over the head or fastens at the back will be a struggle.
Check the nappy access
This is the detail most costumes get wrong. Poppers along the inside leg or a two-piece design save you from undressing your baby completely at every change.
Soft, breathable fabrics only
Cotton and soft knits next to the skin, with any rough netting, sequins, or glued details kept well away from the face and hands. Check inside seams and remove scratchy labels.
Skip hats that do not stay put
Hoods attached to the costume stay on. Separate hats do not. Never use elastic chin straps, drawstrings, or anything with a cord near a baby's neck.
Dress for the actual temperature
Most baby costumes are worn over a vest and sleepsuit. If you are going outdoors, treat the costume as one layer and add a proper warm layer on top rather than relying on it.
Keep the outing short
Twenty minutes of porch photos and a walk to a neighbour's door is a full Halloween for a baby. Plan around naps and feeds, and head home before anyone is unhappy.