My heart is broken

I have looked after granddaughter from birth 5 days a week 7am to 7pm. When she went school i said I would only do two days Tuesdays and Thursdays She is now 6. i have another granddaughter 2yrs who I have I have had on Fridays and who comes on Thursdays but her mum come too. I have a grandsons who is 10 months who I have on Mondays. This tuesday my daughter asked could I have the 2yr old as she was having her windows taken out and it would be cold.and I thought because of age difference and being on my own safety of doing tea while they were here would be too much. So in the morning I txt and said would it be okay not to have the 6yrs old and then the floodgates opened when my son asked via txt I said just to be safe I would not have the 6yr old he said I was stupid and so I was dumping his daughter and she would be upset so I said okay don’t want to take things out of proportion and I would have her then I got the full blown so you are dumping her for the 2yr old granddaughter and his partner said in txt that it was crap excuse and I was dumping her and being over dramatic. I was so upset I just thought I wouldn’t be able to give my whole attention to the 6yr old. I said they have blown things out of proportion and it was a one off. I feel like crying all the time I have her on Thursdays and I am sure they will cancel me.