Hi, My baby is 13 weeks old. I am placing him on his back to go to sleep but he rolls to the side when fallen asleep. Do I need to roll him back on his back? (He wakes when I do, but I’m worried he will roll completely over if left) Also he wears a sleeping bag (one arm out currently with transistioning) I wanting to use a sheet to keep him secure as he rolls around between cycles and wakes. Is there a certain type of sheet I should use or avoid? Also can I use a waterproof mattress protector. Thank you in advance Stacey

What you are describing is normal development.
Most babies will be rolling over by 5 months…....some earlier, some later.
This is very normal as babies grow & become stronger many babies then prefer to sleep on their side or tummy, & often don’t change from that position.

While your son is younger, it is not uncommon for a 3 month old to roll.
Red Nose actually recommends to have baby’s arms out of any wrap at 3 months in preparation for rolling.

Modify the wrap to meet the baby’s developmental changes, e.g. arms free once ‘startle’ reflex begins to disappear which is usually around 3 months
https://rednose.org.au/article/wrapping-babies

If so, it is important to cease wrapping now (or using a bag that keeps arms in) to ensure both arms are free..

This is not something that needs to be stopped, but it is important to make the environment as safe as possible for this to occur.
A light cotton sheet is fine, but there is no advantage to use it as a restraint.
As you son gets older he will most likely move around the cot more, & climb out from under any covers.

Always place baby on their back to sleep.
Ensure cot mattress is firm, well-fitting & flat.
Ensure there is nothing loose or soft in the cot.
Use a sleeping bag now that has appropriate size neck & arm holes.

Red Nose has the following information now that your baby is starting to roll.

Give baby extra tummy time to play when awake and supervised as this helps baby to develop stronger neck and upper body muscles which in turn enables them to roll back over.
Make sure that baby is on a firm and well-fitting mattress that is flat (not tilted or elevated).
Make sure that baby’s face and head remains uncovered (do not use lambswool, doonas, pillows, cot bumpers or soft toys)

As babies grow and develop they become very active and learn to roll around the cot.
At this time, continue to put them on the back at the start of sleep time, but let them find their own position of comfort.
By this stage it is not necessary to wake during the night to turn baby over to the back position

Do not use any devices designed to keep baby in a particular sleep position.
https://rednose.com.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over
https://rednose.org.au/article/is-it-safe-to-use-products-designed-to-keep-baby-in-a-particular-position

When using a waterproof mattress protector, Red Nose has the following information.
......always make sure that the waterproof mattress protector is strong and a tight fit.
Never put soft bedding under the bottom sheet, such as a sheepskin, as this makes the sleeping surface too soft.
https://rednose.org.au/article/what-is-a-safe-mattress