"What guidelines would you suggest for letting toddlers consume fish, especially varieties that may have mercury contamination? Would you wait until the toddler is a specific age to give tuna fish or other similar fish, or serve those fish infrequently?"
After a year of age, I recommend adding fish to your toddler’s diet. There is a lot of different fish to choose from, but you may not know which ones are safe. Two easy ones to remember are: Wild pacific salmon (not farmed) and canned light tuna (not albacore).