Cowbirds in the US will lay an egg in the nest and when the chick hatches, it will push the other babies out, leaving the ignorant foster parents to raise it.
The jaybird was probably going to eat the little guys. I have seen eagles snatch crows out of their nest for 'on the fly' tastey treats.
I see someone on Craigslsit selling worms if you need some or if you want to come to my place you can dig in the compost pile for some. If you get tired of the Momma bird act there is always PAWS to help you out. Since the robins are native they will rehab them and release, just don't tell them the entire story . They fell out of a nest in your backyard. What you did was technically illegal in this State.
This will go no where fast but I have to.
1)The bird isn't your kid. Saving your kid is an option.
2)If you were so concerned about the baby birds why did you leave them to be a potential meal for 2 hours?
3) If you want to argue or debate,I suggest the pm link.