Children are definitely invited. Its a great learning experience. You can walk up starting at 1:00 on weekdays and get available walk-in tickets.
You can get tickets online. Scheduled tickets are months in advance. You may also try for same day tickets at 6:30 AM on the museum's website.
They release the tickets via their website monthly. Please check the museum's website for the next release of tickets. However, this month the museum is doing walk up Wednesdays. Which means you can walk up without a ticket to get admittance into the museum.
All entry is free, always. You csn get timed tickets ahead of time if you go to the Smithsonian website the morning of your visit at 6am. They run out in about 10 minutes every day, so set your alarm and be ready to go. Otherwise yiu can wait in line at the museum.
Tickets become available online on the first Wednesday of each month. Children and strollers are welcome. Children must have tickets also. During the month of April only, you can visit the museum on Wednesday's without timed passes.
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