Nurseries at voluntary-aided schools are facing almost unprecedented demand for places in September, with some receiving five applications per place.
Although it is recognised that parents will make applications to a number of schools, head teachers have expressed concern about the small number of places remaining after siblings have been accommodated.
Simon Goulden, education consultant at the United Synagogue, said a number of issues had impacted on the situation this year.
For instance, the norm among mainstream Jewish families was now three children, rather than two, creating extra demand for places.
In addition, "whatever the size of the family, more and more parents are opting for a Jewish education".
At Wolfson Hillel in Southgate, which is offering 50 places, there are 35 siblings and over 100 applications. Head Jason Marantz said: "We have been highly oversubscribed and we are unhappy that we were not able to accommodate more people. But it's indicative of the fact that people want to send their children to Wolfson Hillel."
In Edgware, Rosh Pinah acting head Judy Greenberg told a similar story. Akiva in East Finchley starts at reception rather than nursery but has the same problem. Head Suzy Stone relayed last year's figures "as Barnet don't send out offers until next month. We had 162 applications for 60 places, of which 42 went to siblings and it's going to be similar this year. We have an ongoing problem of oversubscription and Barnet has agreed to look at additional classes."
Herts school Clore Shalom has 30 places and 120 applicants and the waiting list at Sobell Sinai in Kenton is even bigger.
Jillian Dunstan, head at Mathilda Marks Kennedy in Mill Hill, said the school had received 105 applications for a 26-place nursery, of which 18 would go to siblings.
"There are families almost on the doorstep of the school who might not get in and I don't know where they will go. It would be helpful to expand but we're in a listed building so we can't."
At Barnet Council, deputy leader and cabinet member for children's services Councillor Andrew Harper said: "We are aware of the demand for places in the borough's Jewish schools. We have been able to make small increases for some schools for the 2010 intake which we hope will help address some of the difficulties faced by parents."