Thank you for the question, as with any nutrition question there are always considerations unique to the individual such as health status, special dietary concerns etc. In general pickles can be considered to be a relatively healthy snack yet they are often high in sodium and can be high in sugar as well so moderation is always key. There is no particular concern for children outside of the of general considerations already mentioned. I have selected a couple of good articles that discuss the topic. 

https://www.webmd.com/food-recipes/health-benefits-pickles

https://health.clevelandclinic.org/are-pickles-good-for-you

Thank you for the question.