trying to set up family sharing

my kids have there own ipads and ive tried setting up family sharing a couple time and couldnt figure it out so i just let it go until just last night my daughter had access to my card and spent a lot of money so i am now taking the time to get everything setup. i was wanting to know how to setup that up both of there ipads are set up with there own apple ids now i was wondering if i had to set up another one for them or if i could just put there current one on here. thank you