Special Sergeant Craig Keane, 28, pleaded guilty to nine counts of sexual assault of a child under 13 years at Snaresbrook Crown Court on Monday, 20 February.
He will be sentenced on Monday, 20 March.
Keane was charged on Thursday, 27 January following an investigation led by the Sexual Offences Exploitation and Child Abuse Command.
He has been suspended from duty.
The role of a MSC officer is a voluntary and unpaid.