They recently removed a member of staff from their team and social media platforms after news came to light that they were involved in racist antiques and grooming minors, and have heavily vowed to perform sincere and deep background checks on people they hire to work for them. They are doing their absolute best to keep Club Penguin Rewritten as child-friendly and safe as they can.
This site is perfectly safe, and a great online game for your child (with profanity filters, a great environment, etc.). I will say that it DOES have an older audience than the old Club Penguin, so your child will likely be playing with a large portion of young adults (but as I mentioned before, there are systems in place to prevent significant trouble from occurring because of this).
Club Penguin Rewritten is just like the old Club Penguin. As far as I know, there aren't any ads on the site. However, many of the people using the website are teenagers, so if you let your child on, be cautious of that.