Hi there, Is there an age where children should not be in a sleeping bag anymore.

There is no specific age when children should no longer sleep in a sleeping bag.
I assume you are referring to the type of sleeping bag where the arms are free & not contained within the bag?

It is best to not use a sleeping bag (arms out) when child is moved from a cot to a bed, due to the risk of trips &falls; when child wakes up & tries to walk.
Have a look at Red Nose “Cot to Bed” information here:  https://rednose.org.au/downloads/Cot_to_bed_brochure_for_families.pdf