Please don't ignore some of the more blunt comments because they aren't "kind", mostly people post on the adoption board with experience and because they want to help parents and children.
And you don't love your prospective child yet so any decisions you make now are theoretical.
DS's difficulties didn't show significantly until he was about 7 and when I look back his behaviours clearly showed a problem much much earlier which I allowed myself to ignore because everyone assured me that it was "normal" that all kids show separation anxiety at XYZ age. I look back now and really regret not listening to that inner voice telling me all wasn't fine and compliance from a child doesn't necessarily mean all is fine and dandy.
I think far better to assume that this kind of day will NOT be OK and plan for a gentler alternative like a local park and lunch at home or locally then your father is prepared now and you're not trying to argue with him about it whilst you're exhausted in the early days of placement.
However I can never tell people enough how much I regret certain things that I did in the early years (yes years, not months) after placement because my son "appeared" to be fine with it. Now I have no idea if anything I did/could have done would have made a difference but I have to live with the knowledge that I didn't always do the right thing but the expedient thing (even with the best of intentions) - partly because I was trying to keep everyone happy.
No-one is impuning your parenting skills because a) we don't know you and b) you don't have any yet! Your post is written that you have made the decision to go ahead and how do you keep him entertained, so I don't think you should take offence at those of us who think you should rethink the plans and questioning why you're falling in with what your Dad wants. Even if some of us might be a tad more blunt than others...
And I (and others) can get evangelical about making sure prospectve parents hear our voices in situations like this because it's easy to latch onto those which are saying "well it could be fine" (with a gentle whispered "but it might not") because it's what we all want to believe. But Kristina and I probably between us know hundreds of adoptive families over a 20 year timespan (and if I went back through the thread and picked out those who have said the same thing in a gentler way you could probably add a hundred more) and I'd even go out on a limb to say that the majority of children adopted at 3 would not be fine with the day you describe a few months after placement. A large number might appear to be fine of course but I still think it's not in the best interests of a child when an alternative less demanding day could be planned. You might not even know at the time if your child would cope - why would you take the risk?
And we don't say any of these things to upset you, we say it because it might make a difference to a vulnerable child.
Having said that I wouldn't be planning anything at all in case it tempted fate! Just about everything that could go wrong with DS's adoption did and the timescales stretched longer than I expected as a result.
Sorry that turned into a bit of an essay.