Toddler only eats snack food and milk

I have a 4 1/2 year old toddler that I just got 3 days ago as a foster child.  He will not eat anything other than bananas, milk, cookies, goldfish.  It says he was bottle fed whey protein to meet nutritional needs prior.  I have tried to feed him everything, including shakes and smoothies with protein, but he will not eat anything but the above mentioned.  Any suggestions.

[Renee Radenberg]

His weight is between the 75-50th percentile for his age. He must be eating / drinking something because his weight is above normal for his age. He is drinking milk and eating bananas. Then replace it with your own milkshakes (milk, ice cream (vanilla), and banana blended together) for additional calories and protein for weight maintenance. Remember to relax at meals and just give him the foods he wants. Slowly introduce new foods. Sometimes it takes 5-9 times to introduce a food to a child that they will accept, however, if they do not want it you have to not make a fuss and let it go. The Child Behavior Forum may give you additional information.