You're lucky to have baby robins, we have watched crows take them right as they fledge or are about to fledge every year for at least 10 years. The parents keep building nests under our deck and I swear the same crows come back each year and wait. I can see the crows behavior change as the babies get close to leaving the nest, they start walking the yard, singly but working together, 3 or 4 of them. One year, I had had enough and I was so upset about this that I sat close with a pellet gun, prepared to take out any crow that threatened the fledglings as they were staggering around underneath the nest. In the end, I couldn't do it. Instead, I began chasing them away but they were fierce! One crow actually charged me and wouldn't back down. While I dealt with this, another crow flew off with a baby and then another. Made me sick to see it and I had been defeated. So, these days, I ignore any nests. What will be will be and ignorance is bliss.