They’re strung up and kept, equally securely, at the front (4)
I believe the answer is:
ukes
'they're strung' is the definition.
(ukuleles are stringed instruments)
'up and kept equally securely at the front' is the wordplay.
'up' becomes 'u' (I am not sure about this - if you are sure you should believe this answer much more).
'and' means one lot of letters go next to another.
'at the front' says to take the initial letters.
The initial letters of 'kept equally securely' is 'kes'.
'u'+'kes'='UKES'
(Another definition for ukes that I've seen is " items to play with".)