Sounds like he is resource guarding. How does he react to YOU around his food and treats? Can you run your fingers through his kibble while he is eating? Can you give him a treat or a favorite toy and take it away without him acting out? If he reacts to you as well, you should work with him on that between the two of you first, to desensitize him. Then, (when you baby is older), you can work on resource guarding between the two of them. Meanwhile, don't put her in a situation where he might turn on her. No treats together, no feeding together, no toys.
How to Prevent Resource Guarding in a Multiple-dog Household | Karen Pryor Clicker Training