Heard sea was up to the playground equipment (6)
I believe the answer is:
seesaw
'the playground equipment' is the definition.
(I've seen this before)
'heard sea was up' is the wordplay.
'heard' indicates a 'sounds like' (homophone) clue.
'was up' becomes 'saw' (I can't explain this - if you can you should give a lot more credence to this answer).
'sea' is a homophone of 'see'.
'see'+'saw'='SEESAW'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for seesaw that I've seen before include "Go one way and then the other" , "yo-yo" , "Children's playground item" , "Recreation ground item" , "Up-and-down children's game with plank on barrel" .)