It should not cause problems if you amend your return to remove them as dependents so they can and file in the US for themselves, but don't rush things - amend your return as soon as possible but have the children wait as long as is reasonably possible before filing for themselves.
See How do I amend my 2020 return? for instructions on amending your return.
The children will have to file their returns by mail since you have already submitted a return that included their SSNs - efiling is not an option once a SSN has been used on another return.
The longer they wait to file, the less likely there will be a conflict with IRS records of your earlier return. This is especially true since the IRS is so far behind in processing 2020 returns, and paper returns are much slower to get processed (and have records updated). They may want to consider filing an extension to make sure your amended return is processed before their returns are submitted.
See How do I file an IRS extension (Form 4868) in TurboTax Online?
