i dont think 4 and 2 are a suitable age for a rabbit. they dont like being picked up and tend to scratch and they can leave some nasty marks.
work wise, they are a suprising amount of work, they need to be let out into a play area everyday (bare in mind female rabbits enjoy digging so if ur in a rental or something it can be troublesome) and theyre hutches need cleaning out very regularly to control flies and odours. i do the whole hutch everyweek and the litter tray every second day.

cost wise, an 8kg bag of bunny mix from petstock is $15 my guys get a bowl a day, hay can range depending on the season, but u can pick up a bale for about $20 usually, that being said a whole bale will go stale for one rabbit so u might be better off buying a bag of eating (not litter tray straw, HUGE difference) hay from ur pet shop.
petstock have big cubes of woodchips for about $14 that should last quite a few months with just one rabbit.

if i can help in any other way just ask