Our 8 year old has had 6 surgeries and 1 procedure, beginning at 6 months old, that required us to limit his activity for various periods of time. Yes, it is very difficult but it can be done, even if you have to spend the majority of your time entertaining.
As far as what may be too active at this age, they usually just mean no running, don't take them outside and let them get hot and run around, no jumping, etc. Rides in a wagon or stroller are usually good for these times, even if you have to do it in the house (if you have room). Those plastic lap trays that have a place for a drink,