ETF savings plan for my child from birth – what monthly rate makes sense?

Hello everyone, I will soon be a father and would like to open a savings plan on the Vanguard FTSE All-World (VWCE) for my child from the first month of his life. Now I'm just wondering what monthly amount would make the most sense or rationale - €100? €200? The savings plan is really intended to run in the very long term. Maybe you can also recommend other ETFs that you think are interesting for a very long investment horizon? I already have over €100,000 in the VWC