Gift for a one year old great grandson

I would do memorable. What about a Steiff toy Animal, not cheap but very collectable and something lovely to keep.
I like the portrait idea too.
Enjoy your trip.

I think the tree is a lovely idea but I d be worried that if I bought for three and one tree died it would be awful

Just make sure that if you buy a fruit tree the parents want it and will be able to care for it. Some families don't have a yard and/or don't want to have a yard, or aren't into gardening.

If you would like to buy him a toy, I would suggest either a book or something that he can do on his own - stacking or push/pull toys are a hit at that age. (Just make sure it doesn't make a racket.)

Granny23 - that's a lovely idea.

We gave each of our DGC a fruit tree for their 1st Birthdays. All of them are now flourishing and bearing fruit, much to the delight of the children.

I am sure that you would be able to buy an appropriate tree in Australia and have a wee ceremony to plant it.

What about booking a family portrait?

A ‘Melissa and Doug Wooden Stacking Train’ is a lovely traditional toy and will guarantee many hours of fun.

Perhaps find a beautifully illustrated copy of a children's classic book? Wind in the Willows? Or Winnie the Pooh? Something very English. (Assuming you are English) You can write in a book too.

Picture for his room? One that will be suitable for a child but will not be unsuitable for him as he ages.