How to keep them from being bored?

Firstly hello properly.  I'm a brand new chicken keeper/owner/lover coming up for the week 2 anniversary of having my girls.  An Amber Lee (Sookie), A Black Star (Mrs Peckles) and a Bluebelle (Big Bird).  I worry that they may get bored, they have a fairly spacious enclosure and go free range in the garden every couple of days (once I've done the tedious chook proofing procedure!). Would an 'activity centre' be good?  They rush to the front of the netting whenever I appear, partly cupboard love I'm sure (where's the corn, where's the corn!) but I'm sure it's also because they're mad keen to get out into the garden again.  All advice would be welcome.

They do like to be entertained    I used to rearrange their straw bales for them to keep them busy and gave them a weekly weed pile to play in. Dust bath too of course is required.  They like plants and shrubs to hide in, plastic garden chairs to sit on (I kid you not  )  Mine had a huge viewing window so they didn't miss any comings and goings    they do like a cabbage etc to peck at as well, and a sweetcorn cob will keep them, and you amused, for ages