I've been in this situation.
You just have to ask your boss (or check a handbook or whatever to see) if it's OK. Some institutions will require TAs to keep hands off the undergrads no matter what, others only if you're the student's instructor. Asking the boss would be awkward, but considering you have years to...interact with the female undergrads if it turns out to be OK to do so, it's worth finding out. Do NOT guess. Check.
You just have to ask your boss (or check a handbook or whatever to see) if it's OK. Some institutions will require TAs to keep hands off the undergrads no matter what, others only if you're the student's instructor. Asking the boss would be awkward, but considering you have years to...interact with the female undergrads if it turns out to be OK to do so, it's worth finding out. Do NOT guess. Check.