Science experiments are usually a hit, a pet if the parents permit or airpod type of tech.

For that age I would say something more like an experience.
Maybe go in with other family members for dreamworld passes or something similar

I have a girl who is 9 so I’ll tell you what she loves atm
Books, CD’s DVD’s, Craft, Nerf Rebelle, Clothes, and Smiggle!!! In fact all 3 of my children are totally in love with Smiggle!

Depends on how much you want to spend. Lego, books, water pistols,cap pistols,swords, favourite hero costume, science packs that makes volcanoes, messy goo or explosions. Footballs, skateboards & protection gear to go with it, bike helmet with favourite theme.

Lego in a theme they would like, remote control cars or electronic kits to see how things work,or solar kits, (see dick smiths or jaycar) or woodwork kits.

I give a lot of books and craft type presents. Things like building a volcano that erupts or putting all the bones together of a dinosaur would be perfect for this age group. Places like Toys r Us carry a great range of these type of gifts. National Geograpic is another great shop for this age group.

Games, DVD’s, music CD’s if they are into music. footy stuff, electronics, books, spy gear so they can spy on each other lol.. Good luck.

Lego kits always seem to go down well with boys.

We did a experience for our 10 year old he went to the zoo and got to do the night sleep over, he loved it and we are looking into other experiences for him to do

i know most girls are into loom bands at the moment and my 10 year old nephew is into mindcraft hope this helped

gift cards are good but all kids love getting real presents

Nerf guns for outdoor play. Or the nerf crossbows.
Not harmful and loads of fun.
If they both get a set then they always have someone to play with.

outdoor toys are usually good eg soccer ball, cricket set

Skate boards, helmet and knee pads

a basketball hoop, ball and soccer net, or some kind of outdoor toy. Or you can buy them vouchers to a particular activity they would like to do.

Remote control cars for both to play with?

movie tickets, or tickets to a show they wanted to go too