
Are childish projects a red flag in resumes? Read context of childish
For example if you are a data engineer you built some data project witn Pokemon data . You are a full stack engineer and built a batman themed portfolio
Yes, unless you built them for an actual business case for an employer or client.
For example, if you worked for Hamley's, and you built a website for a promo campaign for the sale of Batman toys coinciding with the launch of a Batman movie, then it's acceptable. Because it shows you're an adult and a professional, doing the necessary work to help the business of your employer.
If you built a personal project with Batman or Pokemon data, your potential employers will just doubt whether you can behave as an adult & a professional working in their business. So that's not acceptable.
As a general principle, all businesses and companies are money-making machines, and you're applying to become a cog in that machine. So anything that signals that you are an adult & a professional who understands their business and will help them make money, that's a positive. Anything that detracts from that message, and looks childish, is negative.

Well I have a comprehensive EDA project that derives insight from football data, I think that much is fine? Sort of like moneyball analysis