Hello!
And "Thank You" for your post! Your question is a very good one. I think a children's book consultant can provide solid feedback. I would ask three questions to determine whether a specific individual might be able to provide you with constructive feedback. How long has this individual been a children's author? What kind of track record does this person have (in terms of sales, contracts, brand visibility)? Does this individual write in an area of the children's book market (in this case, picture book market) that is similar to yours? Another way to get some great feedback is to develop a relationship with a local children's librarian or educator. Provide some free prototypes to the classroom or library and ask for some feedback from them and their students. This type of feedback might be less expensive and just as valuable.
A word of caution here...always look for value and get something in writing before hiring someone at an expensive hourly rate. Get references from others who have hired them as well before spending your hard-earned money. And always take everything with a grain of salt. Before changing your book, ask yourself the question: Will these changes really improve the book? If you can step outside your ego and answer "yes" to that question, use the feedback in a constructive way to improve your book.
