Is time travel possible?

Todays dinner discussion on time travel (with a 12 and 14 year old)

Fritzie (14 year old): we can only travel into the past as tourists. We cant change the past. The future does not exist because there are an infinite number of future time lines.

Diego (12): Time travel exists. Don’t know why.

Me (52): Nobody knows when now -the present- begins or ends. Because of that there cannot be any future or past.

What do you think? Can we travel in time?