Highchair surface (4)
I believe the answer is:
tray
'highchair surface' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tray that I've seen before include "Item used for carrying food and drink" , "Flat carrier" , "Informal meal" , "Shallow receptable for carrying something" , "'It's used for carrying, crockery say (4)'" .)