I'm a little late starting this entry cos I've been Pawley over the last few days but I had noticed a few people talking about Headspace which I know I touched on in late February.
I think the first thing I will say is this space is very much as you, yourself make it and you do need bring something to being in it even if you may be fortunate to have either a Caregiver do things with you or you go to any number of littles activities where organizers do lay on activities because you're the one 'doing' them to getting into that sense of being more child-like.
Because anyone for a host of reasons isn't able - and I do understand - to get out either as much as they like or at all due to lack or disabilities perhaps doesn't mean you are unable to but you'll need to create them where you are.
The second thing is, to do this we need to remove as much 'groan up' mental background noise as we can, not just technology (sometimes super intrusive) but also anything that distract us from playing in the way as kids we did.
If you can add a few touches like cute 'throws' (aka Covers) over furniture, I'd suggest bringing out the one thing you loved from your childhood first and putting it in your room unless you're fortunate to have a already set up play space.
It may be a favourite plushie, a teddy or doll you hugged, talked to and created adventures with. I can't speak for you but you may of played at being a Vet, a Nurse or an Astronaut with them but we're going back in time and buried away are just the memories you need to get back to where you were.
Some people like something a little less imagination centred but fun nonetheless such as watching a Disney movie or cartoon series that they find takes them back.
The other approach may appeal to those of us who like difficulties aside to do art to draw, colour or paint but allowing our 'inner child' to tell us and in way do the activity that relates to their interest and age range which is something personally I feel matters for your own well-being.
Some find littles role playing games and sites helpful in getting into that 'role' opening up your inner childs thoughts and expressing them with others.
The important thing here is you do create that space to go back, enjoying the experience.