The children represent those who were living in poverty, with no hope of improving their lot due to lack of education and lack of opportunity. The Ghost of Christmas Present was sheltering them as representatives of all those who were discounted and decried by Scrooge. Instead of contributing to charitable organizations that could help improve their lot, Scrooge's action was to ask "Are there no prisons?...Are there no workhouses?"
The Ghost reminds Scrooge of his unfeeling words after warning him of the consequences to all of Scrooge's society if the children, and the life conditions that they came from, continued to be unaddressed.
Beware of them both,...but most of all beware this boy (Ignorance), for on his brow I see that written which is Doom, unless the writing be erased.