Cute pics, love your donk's coloring! Good for you guys for picking them up. Certain types of walnut trees can be very poisonous to horses. Black walnut in particular, the entire thing can be toxic, leaves, bark, nuts & the roots can even be strong enough that the ground around them can even cause problems. Not sure if you have black walnut is Australia or not but thought I would add that.
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.