The mas'alah is that a gift given by a non-bāligh child is invalid. However, in our age, it is common for children to give gifts. In fact, children are often encouraged to do so, so that they learn generosity etc.
Have any contemporary 'ulamā reconsidered this mas'alah?
I have heard the suggestion that a father can teach a child generosity by making him a wakil to give from the father's wealth, but that doesn't solve cases where the child e.g. wants to share his own toys or sweets with friends
مجمع الأنهر في شرح ملتقى الأبحر (2/ 353)
[شروط صحة الهبة]
وشرائط صحتها في الواهب العقل و*البلوغ* والملك
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
It is indeed correct to believe that the giving of a gift by a non-mature (non baaligh) child or a majnoon (insane) person will not be valid. The reason is that both of these groups do not have the allowance to own any property.
If, however, a child is encouraged by the parent to share their toys etc. and the sharing takes place with the permission of the parent, then this will be valid. This is because the child has now received the allowance to give from the wealth of the parent – who is the actual owner of the toys – not the child. The guidelines of the shariah state, ”It is not permitted for anyone to perform any transaction in the wealth of someone else except with their permission.”
The wealth, in this case, will be in the form of the toys/sweets and the actual owner is the parent of the child. The child then receives permission to make transactions by sharing through the permission of the owner.
Only Allah knows best
Written by Maulana Naieem Mohammed
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Badai’ us Sanaai’,pg 109,vol 8 Daarul Hadith Cairo 2005
 Qawaaid ul Fiqhiyya,pg. 99 # 82