We all say 'I love you mostest' even the kids. But, its not about 'most compared to someone else'. Its 'most compared to the possible amounts of love to give out.
Even the kids say it, to each other and all three of us. Its our way of saying that if there are ten levels of love (for example) we are giving all ten. We can give 100% effort in one class or we can give 100% effort in every class. We can give 'our all' in one class or in every class. Likewise, we can give our all in every relationship.