Istanbul / Area for tourism w 2 year old kid

hello dears!
as we now have direct flights from Kathmandu to Istanbul i am planning to meet up with a friend from other side of europe in mid october. I would be travelling w my 2 year old boy. i was wondering if we should book our accomodation in a specific area of town where there is kids fun incl parks and playgrounds but still nice and exciting for adult tourists.
Further, would you have any tipps on where to go NOT too far from IST, best on train or bus rather than flight to a either countryside (agritrouismo style) or seaside place. we will have max 9 days in country, so not too packed.

thank you so much for suggestions and if you plan to come ktm will try to assist as well!!

warm regards, kathrin