Generally we see that Brahmopadesam is performed to a male child and thereafter he becomes a Brahmachari. He is then asked to perform Ssndya Vandanam and chant the Gayatri Mantra thrice a day. However, he is not introduced to the meaning of the Mantras unless he being a bright child, on his own. tries to understand through Google or whatever.
If such a child is introduced to the Gita and is advised to do all action as worship to god without expecting results and the child shows interests and intentions, will doing Sandya Vandanam without knowing the meaning be beneficial or following Gita will be more beneficial to the child.