Oh gosh, you poor things.
It is so easily done. My LO was scalded at 6 months by boiling water too. It wasn't as big as that but it was on her hand which obviously has joints and skin that needs to stretch etc, so it was very worrying. We saw the plastic surgeon the next day who said the same thing as you were told, but because it was a smaller burn they were more hopeful we would avoid any more intervention (and it did).
It was so swollen and sore looking, especially the next day, I felt absolutely terrible. We used a dressing called mepitel, which just from looking online seems to be pretty similar to biobrane.
My LO was fine in herself the next day, we kept up with the calpol & ibuprofen and her whole arm was covered with a bandage, but she was in good spirits. In fact it worried us more because we were thinking, "It must have damaged all her nerves and she'll never feel again" but the nurse told us that if you keep up with the calpol (think we just did it for three or four days) it is a very effective analgesia, and also that because the mepitel (and biobrane) are really good for reducing pain too because they keep the area moist and in the right position (so it doesn't get all tight and painful when moved).
The worst part for me was seeing my LO in so much pain. She cried and cried and cried and cried, she cried for hours until she passed out in our arms. I'm sorry that you probably had to go through a similar situation.
I am sure you know this already, but you should be extremely vigilant for signs of infection. I would say that with a burn that size, if your LO gets a temperature, I would take them to A&E immediately even if you think there are other symptoms of a normal cold. I am sure you know that already. In fact, I wondered about it when I was taking my LO back for check-ups, so I asked the nurse, "How will I know if she has a temperature because the burn is infected, or because she has a snotty nose and a cold", and the nurse said simply, "You won't so go to A&E straight away". In terms of looking after our LO, we were told that was pretty much the most important/only thing we needed to do. The wound was covered and safe with the burns dressings, and our job was just to watch for signs of infection.
After 14 days, the burn was healed. It was still red, but it was new skin. Looking at your picture, I don't think yours is any deeper, although it is bigger. There were a couple of splashes on my LO's arm which were about the size of the splash on your LO's other foot. They were completely gone after 2 weeks, maybe just a bit discoloured, but the skin was absolutely fine and new. The worse one was on her hand, and it did take the full 14 days to heal and was very dry afterwards. We put e45 on it a few times a day for the next few months and now (a year later) it is totally gone.
I'm sorry I can't be more help. It's a horrible feeling when your Lo is injured and you just have to 'wait and see'. Keep up with the protein. I'm sorry you have been through this. xx