Is Monday 3rd September Still Busy?

I have a 5yo son who goes back to school on Wednesday 5th Sep and my daughter turns 2 on 3rd September. DH has the day off work and we wanted to have a day out together. I was under the impression most children returned to school on the 3rd but at my DS’s school they have 2 inset days so they are late going back.

I therefore thought that we might be able to enjoy a fabulous day at either Paultons or Legoland with minimal queues, however both are operating their summer hols opening hours until Tuesday 4th.

So my question is - are lots of children still off school on the 3rd? If we venture to a theme park are we going to spend the day queuing?

Thank you for any responses!