Just be aware that there are 2 types of trains between Amsterdam and Brussels;
1) Thalys; the high speed train. Tickets for this train need to be booked in advance and are tied to a specific train on a specific day and time with reserved seats. In Brussels, this train only stops at Brussels South, (Bruxelles Midi in French, Brussel Zuid in Dutch/Flemish)
2) Intercity Brussels; a regular train. Tickets for this train are only tied to a specific day. On that day, you can take any Intercity train from Amsterdam to Brussels. In Brussels this train stops at Brussels Airport, Brussels North, Brussels Central and Brussels South.
Tickets for both types of trains can be bought at the website of the Dutch railway company https://www.nsinternational.com/en/out-and-about/brussels-for-a-day