I'd suggest getting in a reputable behaviourist who can assess the extent of your cocker's concern, and also give help and advice as to how to get the dog to relax with the child present

. I agree the problem is likely that there is fear due to the toddler "toddling" and being unpredictable. Escape routes are vital,as previously mentioned; plus not allowing the toddler to go after the dog in any circumstance. You will need eyes in the back of your head!
I suspect at the moment the dog is under pressure and the only problem is, if he does not feel his grumbling is taken notice of, his warnings may escalate. The same thing might happen if there is any additional stress in the house which adds to the dog's stress levels. I'm not trying to worry you - it may well be that it will stay at this level and when your little toddler is older, all will be well

For a reputable behaviourist, try www.apbc.org.uk If you do go down this route, please don't just use anyone - as anyone can call themselves a behaviourist these days.
Good luck
Lindsay
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