The answer to your question can be learned from the words of the Rashba here as explained by the Rosh Yosef (written by the author of Pri Megadim).

1. The Chidushei ha'Rashba here cites the Gemara in Yevamos (104b) which says in the name of Rebbi Yanai that the reason why a deaf and dumb man or woman may not perform Chalitzah is that the Torah states that the man and the woman must speak (Devarim 25:7-8). Similarly, the Gemara in Yevamos (105b) states that the reason why a minor may not perform Chalitzah is that the Torah states that a man is required (Devarim 25:7). The Rashba asks, why does the Gemara in Yevamos not say that the reason why the deaf and dumb, or the minor, is invalid is that they do not possess intelligence (Da'as)? The Rashba answers that if the Gemara would have said that the reason why the minor cannot do this is that he does not possess Da'as, we would have said that a 9- or 10-year-old minor, who does possess Da'as, may perform Chalitzah. Since the Mishnah in Gitin (59a) states that young children can sell Metaltelin (movable objects), one might have thought that a child of this age also may perform Chalitzah. This is why the Gemara in Yevamos (105b) states that an adult is required.

2. The Rosh Yosef in our Sugya (beginning of page 62) writes that we learn from these words of the Rashba that when the Gemara states here that a minor possesses the element of Ma'aseh but does not possess Machshavah, this means that if he is about 10-years-old and therefore capable of making a transaction, he also possesses Da'as. Chalitzah is an exception because the Torah explicitly requires an adult for Yibum.

3. Accordingly, if he is 10-years-old, he also possesses Machshavah as well as Ma'aseh.

Kol Tuv,

Dovid Bloom