1.) Xking, Ron, XR2 and Barzo all very similar, and all cope better than you’d expect with mixed conditions. A proper mud/soft conditions tyre is never going to cope well on trail centre hardpack. Not ideal in proper muddy conditions, but that’s the compromise you make for nice rolling speed.
2.) Not a parent myself, and maybe i’d have a different outlook if I was, but no kneepads for XC racing and the bulk of training – only if specifically targeting a session working on technical skills/features.
3.) Some clip on mudguards – make winter XC far more pleasant.
Some water repellent tights/leg warmers (watching muddy puddles bead on the surface never gets old).
Camelbak with spares and mini first aid kit for training.
Phone to call the parent taxi when you’re cold, wet and have just gone OTB for the 3rd time in 15mins.
Waterproof shell to wear whilst waiting for the parent taxi to arrive