I agree - take the money but make sure you don't run up more debts - that's the best gift you can give.
I think the interest thing is something to do with days in the month. Mine all went down alot in March after the short February, then back up in April after a long March.
I have just figured out which child I will be bailing out later in life and which I won't...
I have ynab categories carrying money, ie for road tax (£110), Christmas (£150), holiday spends (back up to £175 after a payment today - all moderating money goes in there without exception), and various other little pots - even a haircut one currently at £8.
So, bank balance £450ish when yesterday's big spends clear. But went to the supermarket for a few bits and said "I have only got £7.36 to spend". Youngest is confused. He saw my balance yesterday and knows we didn't spend it all. I explained about the ynab categories, and said there's just £7.36 left in groceries and nothing left in general spending due to unexpected dental bills, so that's it until Friday. We have food, petrol, there is nothing we need so that is fine.
Youngest thinks it's stupid. He says why ration myself to £7.36 when I have all that money? Eldest totally gets it "If she takes money from Christmas she'll just have to pay it back next month, stupid!"
I have some work to do with youngest I think!
Incidentally, got all the bits we needed for £7.15 