There's no single rulebook for baby clothing sizes. Every brand builds its own size chart, and a '0-3 months' label from one company can run narrower or shorter than the same label from another company. Age-based names are rough guesses at best, since babies grow at wildly different rates. A lot of the confusion that makes parents search for whether muslin clothes run big or small actually comes down to which brand's chart they're looking at, not the fabric itself.
Fabric plays a part too. Muslin cotton is woven in an open, loose weave, which is what makes it breathable and quick-drying, and that same looseness means it drapes a little differently than a tightly woven knit. Epic's pieces are double-layer muslin, pre-washed before they ship so they arrive soft instead of stiff, and they keep softening with every wash at home. Wash cold on a gentle cycle, and skip the fabric softener and high heat, since both change how the weave feels over time.
Because every brand measures differently, the safest move is to check actual body measurements rather than trust the label alone. That's the same habit that helps dads figure out what size to buy for a baby when they're shopping without a clear reference point. Epic's sizes run roughly from newborn to 4 years, and when you set them next to mass-market baby clothing, the cut and sizing habits can look different right away. If something still doesn't fit the way you expected, Epic ships worldwide with tracked delivery and takes unworn returns within 30 days.