My doc said the same thing as the lady above if your already used to it you'll probably be fine however you'll be more tired than your used too. I also started having to use a support belt after 22 weeks or so it helped alot. Just talk to your doc about it and they will help you keep an eye.
If it's normal for up to be on your feet that long before pregnancy it should be okay. I was a toddler teacher at a daycare with my first and my OB said since it wasn't a new thing the long shifts (10ish hours) and lifting/chasing wasn't an issue.
It's your first trimester though so be prepared to be extra tired.
As your belly starts to grow it may become an issue. Just keep your OB/midwife informed of how you feel and they will let you know when to slow down:)
You might be a little more prone to developing varicose veins in your legs if you're on your feet for that long with little to no breaks.