This is the divine lime marmalade that the munchkin is loopy about!
5 cups / 1.2 litres water
6.5 cups / 1.3kg sugar
Slice the limes thinly, saving any pips. Tie the pips in a cheesecloth bag and place the bag in a large non-reactive pan with the finely sliced lime. Add the water to the pan and bring it to a boil. Turn down to a simmer and simmer for 2 hours, stirring occasionally. The lime peel should become very tender.
After 2 hours, remove the bag, allow to cool, and squeeze out into the pan.
Warm the sugar and add to the pan, bring to a boil for about 15 minutes until you reach the setting point, 220F, 105C.
Unless you have litmus paper or a pH meter to check the acidity, assume that this is a low acid food and pressure can for 10 minutes.