Is it permissible to wait until money is available to return stolen goods, and is it possible to collect money from one's allowance to return it without the family's knowledge, and is the embarrassment of asking for forgiveness considered fearing people more than fearing Allah?

You bear no sin for what you stole before reaching puberty, but you must return it. The lifting of the pen from a child entails the lifting of sin, not the lifting of guarantee. You must estimate the stolen items with an amount that you predominantly believe will clear your conscience. The funds remain your responsibility even if you become insolvent. It is permissible to return them from your allowance, and it is not a condition to inform the owners of what you did; rather, the obligation is to deliver them to them by any means. As for your feeling of shame in seeking forgiveness from the rightful owner, it does not mean that you fear him more than you fear Allah.