I have a question, we have an issue with a implementation that creates childs into parent customers, but looks like we found a limit, does anyone know if there's a limit for sub customers?

What's the limit you think you are hitting?

10k subcustomers

In what world do you need 10 thousand subcustomers?

Just for fun i looked numbers up: https://www.statista.com/chart/10117/the-most-common-retail-stores-in-the-us/

My company has a customer with almost 100k subcustomers. My company works with Rental Companies and their Customers. It was before my time but my company, or a consultant on our behalf, reached out to NetSuite because we hit that 10k limit and they increased our limit. One downside to having so many subcustomers on a single entity is that it will increase the load time for that entity's record unless you have the preference 'Delay Loading of Sublists' enabled. That can be enables by a user individually or as a company general preference.