9-11 year old boys are at a pivotal point in their development both emotionally and physically. Many are already at puberty and really don't know what to think about all of the physical changes, some are not noticing changes themselves, but see the changes in boys they interact with and aren't quite sure if they are "behind" or "ahead" of their peers. Not much attention is spent on this issue with boys the way it is with girls, because girl's development is much more noticeable and, in this day and time, more publically talked about. I say all of that to say that what he probably needs the most is time with his Dad to spend together doing something just for the two of them. Have whatever traditional family celebration you normally have, but let Dad suggest to him that he choose his "gift" of whatever he would like to do (just he and dad) together, movies, sporting event, dinner out, fishing, etc. (that is within your budget). Kids are so smart, and more than likely he knows his mom is trying to "buy" a relationship she simply cannot provide. Buying more things or trying to find/create a new interest for him just won't work. Once he feels secure in his "impending manhood" (I know it sounds dramatic, but can't think of a better term", and knows his bond with his Dad will only become stronger as he matures, he will feel more secure in trying mor things and becoming his own person.
I'm the mother of 5 sons, now ranging in age from 17-26, and one grandson, age 4. They have a terrific dad, and even though they are all very different, matured at different rates, etc., one thing they all needed and looked forward to was their own bonding time with Dad. After the first/birthday outing, they will more than likely want to have more time like this and can do something small once a month or so. One more thing...you know how men are...a little squeamish at first with getting the boys to talk about sensitive issues, but encourage your husband to be open, flexible and to try not to hyperventilate when the subject/question goes in "interesting" directions.
I assure you, this type of bonding with his Dad will strengthen the bond between your step-son and you and your daughter as well.
Children are truly a gift entrusted to us by God for a period of time. It truly takes a special person to be a part of raising a child that is not their own biologically; God has chosen you for this special blessing
Prayerfully,
L. K