Solved please help identify this sad tree

hi all,

i'm new here and tbh very inexperienced and not at all green fingered, but would love some advice regarding a tree in my garden please! Its much climbed by my very young boys so would love it to get bigger and healthier if possible..

Anyway is isn't doing so well, particularly on the path side where it is overshadowed by a successful neighbours tree. I think it is a sycamore but not really sure.

I need to figure out what the fungus/disease is and if it is past the point of properly recovering but I guess the first step is to identify what it is.

any help much appreciated thanks!

 

That's Lichens, not fungus.

 

Thanks Scrungee!
Looks like Lichens is not harmful and so not the reason its doing so poorly

 

Looks healthy to me, as said it being overshadowed so struggling to compete for light.
It is a maple, Acer of some kind.