Time spent is the best investment you can possibly make in cementing a relationship with your child. Each child has diffeent needs, so you need to be flexible. One may want to go shopping to a mall, the other may want to eat out, the other may want to go driving. I have a 1/2 daf seder (using the Dial-a-Daf CDs) with my 14 year old, but not with his older brothers (who have 15 hour days in Yeshiva, as it is.
As long as the child in question knows this is his or her time, it will be banked for future reference. In one of the magazine suppliments that cam with either the Mishpacha or Hamodia Pesach issues, there was a story about a foster child that moves in with a family and its impact on the bio kids. Great story and very well written, but the prine line was from the social worker who tried to explain why foster kids need special handling.
As the average kid grows up, the parent makes periodical “deposits” in the affection bank. Attending a chumash party, sending a postcard to camp, ect. So when the occasional “withdrawl” needs to be made (disipline, saying no to a request, ect) there is what to draw against.
Foster kids often come on to the scene with a “deficit account” (negelct, abuse, zero self esteem, ect) so they need to be handled with care.
My point is, MAKE LOTS OF DEPOSITS (n the form of compliments and time spent) EARLY, so you have from what to draw from should the need arise