The younger children would enjoy Cannon Hall Farm and Eureka, both about 30 mins from Golcar. Kirklees Light Railway too, a bit further - 40 mins? Is it October hslf term? They will have Halloween trains in, but you need to book well(weeks) in advsnce. You could pop down to Slaithwaite easily from there and then walk along the canal/train/drive to Marsden and take a canal boat trip through the longest tunnel in England (or something like that!) and pop out on the other side of the Pennines. I can’t remember if it’s Slaithwaite or Marsden that has the cafe on the canal boat. Marsden has a great ice cream place, Sundaes, although I think I may have read that it was closing?
Yummy Yorkshire at Ingbirchworth has definitive not closed, dues superb light meals and fabulous ice creams. Could combine a trip here with a walk round Ingbirchworth Reservoir.
Nice walks around reservoirs at Blackmoorfoot, Digjey, Langsett, Wessenden (not sure if you can walk round this one, next tried. @HoppingGreen might know) and Scout Dike. And Ogden Water.
There is a museum about the Woolen industry in Huddersfield in Golcar - Tge Colne Valley Museum.
Sports centre with splash park in Huddersfield town centre (book in advance to ensure you get into splash park). It also has a climbing wall and beginners taster sessions.
Holmfirth (summer wine country) and Uppermill good for pottering, independent shops and cafes. The Oil Can Cafe in Scholes (near Holmfirth) is great fun! 50s themed with lots of vintage cars on display (wife runs the cafe, husband restores old cars).
A bit further afield, the Yorkshire Sculpture Park is a good day out in fine weather. £10 or so to park, but free entry.
In Halifax, the Piece Hall will interest the adults. Also not far from Lister park of Gebtkeman Jack fame. It’s close to Eureka for the little kids.