One thing worth doing is adjust the sleeping environment. Reduce the number of soft toys to just their favourite, but make sure that one's in bed every night.

Drop the light and noise level by getting proper blackout curtains up, or get a low glow nightbulb or some ambient noise going on. Find what level of noise your child prefers.

But the key thing is consistency. They need to see their bed as their space. It is more worthwhile *YOU SLEEPING NEXT TO THEIR BED* than them sleeping in your bed, unless you have the capacity to sleep through them.

Another thing to try is to spend some time during the day reading to them while they're in their bed, so they start thinking of their room as a nice place.