The one-year-old girl was pronounced dead at the scene, while the young boy was rushed to Emergency.
Despite treatment, he died in hospital.
A 40-year-old man was also hospitalised with stab wounds and police say all three were known to each other.
The Met Police has launched an investigation and no-one else is being sought in connection with the attack.
Redbridge Council leader Jas Athwal posted on Twitter: 'Earlier today there was an incident in Ilford. Two young children have passed away & an investigation is ongoing.
'My thoughts are with the family and wider community who are grieving this unspeakable tragedy.'
