Apps for a 3 year old

[cairnterrier]

I have to entertain DS aged 3.4 for 6 hours at hospital tomorrow (food allergy challenge). Can anyone recommend any apps that he might like as something else to pass the time? He likes Zoo Train and one of the phonics ones. He's particularly fond of robots, trains and tractor Ted. We've already got a drawing one as well

Can anyone recommend anything?

Thanks

Anything by toca boca, but sounds like he would particularly enjoy toca train and toca robot lab. Keeps my 3 yo entertained in meetings.