TL;DR

• Knowing when to lower the crib mattress depends on milestones, not a baby’s age in months.

• Highest setting for newborns, middle once rolling or sitting starts, lowest at the first pull to stand.

• Lower the mattress at the first sign of a new skill, before it is mastered.

• Health Canada’s SOR/2016-152 keeps the mattress support within 7 degrees of level at every setting.

Knowing when to lower the crib mattress comes down to watching a baby’s development rather than the calendar. Kido Bébé’s Montreal team walks new parents through this at every crib fitting, because the timing matters for safety. This guide covers the three standard settings, the milestones that signal each move, and how it ties to Health Canada’s crib safety standards →

Why Mattress Height Matters

Mattress height decides how much crib rail stands between a baby and the floor. With the mattress high, the rail is effectively short, which is fine for a newborn who cannot move but risky for a baby who can push up or pull to stand.

Every centimetre of mattress height is a centimetre less rail to climb over. Lowering the mattress at the right moment keeps the rail tall relative to the baby.

The Highest Setting: For Newborns

The highest mattress setting is the starting point for a newborn who cannot yet roll, sit, or push up. At this height, the mattress sits close to the top rail, which makes lifting a sleepy baby in and out easier on a parent’s back during those early months of frequent feeds.

The position is safe only as long as the baby cannot move independently in the crib. The moment that changes, the highest setting has done its job.

The Middle Setting: When Rolling and Sitting Begin

Once a baby can roll over, sit up without support, or push up onto hands and knees, the mattress belongs at the middle setting. Any one of those skills means the baby can shift position and raise their body higher than before, which shrinks the usable rail height at the top setting.

Many babies reach this stage in the first several months, but every timeline differs. For when to lower the crib mattress, the skill matters more than the calendar.

The Lowest Setting: When Pulling to Stand Begins

The first time a baby grabs the rail and tries to pull up, the mattress goes to its lowest setting. That move should happen at the first attempt, not once the skill is mastered, because a baby who can stand with the mattress still raised can topple over the rail.

The lowest crib mattress setting puts the maximum rail height between a standing baby and the floor, and it is where the mattress stays until the crib is outgrown.

How to Physically Lower a Crib Mattress Safely

How to lower a crib mattress varies by model, but the safe sequence is the same:

1. Take the baby out of the crib and settle them somewhere safe in the room, awake.

2. Lift out the mattress so you can see the mattress support.

3. Follow the crib’s manual to move the support to the next bracket or hook position.

4. Check that every fastener is tight and the support sits level before replacing the mattress.

Signs It’s Time to Move Down a Level

The signs that a baby is ready to sit up in the crib also tell you when to lower the crib mattress, and they usually appear during play. Watch for:

• Pushing up onto hands and knees

• Sitting without support, even for a few seconds

• Rolling confidently in both directions

• Grabbing the rail and trying to pull up

Any one of these is the cue to drop to the next lower setting. Do not wait for the skill to become reliable.

Health Canada’s Crib Requirements That Support Mattress Safety

Health Canada’s Cribs, Cradles and Bassinets Regulations, SOR/2016-152, set structural rules that work alongside the milestone guidance above. One requirement covers the crib mattress support angle: in Canada, the support must not exceed 7 degrees from horizontal at any height setting, so the sleep surface stays level whichever position you choose.

Combined with a mattress that fits the crib’s interior properly, that requirement supports safe sleep at every stage, from the highest newborn setting to the lowest one.

Shop at Kido Bébé Montreal

Mattress settings and hardware vary from one crib to the next. At Kido Bébé’s showroom, 4100 Boulevard Thimens in Saint-Laurent, the in-store team can walk you through a specific crib’s height positions and how its support adjusts before you buy. Every crib in Kido Bébé’s crib collection is offered to meet Health Canada’s SOR/2016-152, and as an authorized retailer we can confirm which models suit your nursery. Visit in store or browse online.

Getting the Mattress Fit Right at Every Height

Height is only half the fit question. An undersized mattress leaves a gap along the sides at every setting, not just the highest one, and that gap is an entrapment risk for a small face or limb. Under SOR/2016-152, the space between the mattress and the crib sides must not exceed 30 mm.

Match the mattress to the crib’s exact interior dimensions, push it to one side, and check the gap on the other before the first night.

What to Remove From the Crib as Your Baby Grows

A crib mattress height guide only works if the crib itself stays bare. As mobility increases, a baby can use anything inside the crib as a step or a handhold, so remove:

• Crib bumpers, which double as a foothold once a baby can stand

• Pillows, loose blankets, and plush toys

• Any mobile hung within reach of a sitting or standing baby

Keeping the crib bare matters at every mattress height, not only the lowest one.

When to Consider a Toddler Bed Instead

Mattress height has a limit. Once a baby can climb out of the crib even with the mattress at its lowest setting, lowering is no longer an option, and it may be time to move to a toddler bed.

That decision is separate from the crib mattress height guide above and depends on the individual child’s climbing ability rather than a fixed timeline. A convertible crib that becomes a toddler bed makes the switch simpler when the day comes.

Watching Your Baby, Not the Calendar

The question of when to lower the crib mattress always comes back to what a baby can do, not how old they are. Rolling and sitting call for the middle setting, the first pull to stand calls for the lowest, and acting at the first sign of each skill keeps the rail tall enough to matter. Ready to choose a crib? Visit Kido Bébé in Saint-Laurent or shop the collection online.