Can anyone suggest any activities during the kids holidays, tried looking on Sheffield City Council website but couldn't find much. TIA

Try this

http://www.sheffinfolink.org.uk/

Don't know how old your kids are, but we're planning Cannon Hall farm, poss Sundown adventure land, poss Ski Village adventure mountain (if it's open), kite flying on Bolehills Walkley if windy, swimming etc...