Hamsters need a much bigger cage than people realise. Google Hamster heaven. That's the minimum requirements. A fish tank style is fine but make sure there is plenty of ventilation. I have always has wire ones with a deep base ire Tgeres zoozone 2 is fab but you would need to.mesh the top to stop escapes .
Re. bedding. Woodshavings aren't great. Carefresh is fab but quite pricey. Lots of people like megazorb but it can be tricky to get hold of. No cotton wool type bedding! Shredded toilet paper is a firm favourite with lots of hammy owners and its cheap.
If your getting dwarf it may be tricky fir a 5yo to handle. A Syrian would be better imo because there is a bit more to them and they are generally a tad slower.
If you do end up with a dwarf then get dwarf hammy food and be careful if sugar contents because they are prone to diabetes.
You need a decent size wheel. The ones sold with cages are far to small . As a rule the hammy should very able to run flat with no curve in the back. Karlie wondering wheels are the best I have found, wooden, almost silent apart from the patter of feet.
Hammys are nocturnal so very prepared for a bit of disappointment if he can't be seen in the day. Mine have always been training d to get up at 6ish by tapping on the cage and feeding.
Lastly - if you get one, get one for you! You will be cleaning, handling etc when your ds gets bored ire loses interest which there is a high chance he will. I have 2 Gpigs (which are by far the best child's pet-worth looking into) and a hammy . They are mine. Ds (4) like to help and cuddle but not very often. Never get a child a pet unless you want it just as much!
If I think if anything else i will be back!
Try www.hamsterfanaticforum.com its fab for advice and pictures of cages etc!
Good luck !