None of us should feel guilty or be made to feel guilty for not being able to help as much as we would like to. None of us do it on purpose, having illnesses or disabilities and if family members don't understand then it is their problem and not ours.
The number of Grans and Grandads on here who do childcare is amazing and should be given gold medals! But it should not be taken for granted by adult children that we will take up the slack when they have children and need to work. It should be worked out beforehand and, if a problem arises healthwise, then the childcare arrangements should be looked at again and the parents should have a plan B in place, just in case. We have done our rearing and should be reaping the benefits of being able to sit back and enjoy grandparenthood, not be, in my opinion, the main carers. It is our time to do a bit of what we please, we have earned it. It is exhausting to bring a baby up or to look after for a short time depending on energy levels.
Cher You need to find ways in which you can spend time with your little ones but keep your health as good as it can be, like Galen said, reading is a good one or on a tablet if older, maybe. Get a little table that can be used where you sit, slide under the furniture and do some little jigsaws or board games or play snap or colouring books. Play 0's and X's with older GC or hangman with pen and paper. Play "guess that tune" with a cd they know. Sing along to some nursery rhymes on a cd, depending on age. Just please don't feel guilty, it is a worthless emotion because it gets us nowhere. Believe me I've had a little over my dad dying even though I tried to do my best, there is always room for guilt. Take care and look after yourself. And to everyone else suffering in some way, be good to yourselves, we are very important people.