Seventeen primary schools had more than half of their Primary 1 places filled by siblings of current pupils after day one of the first phase of registration.
By the end of the entire Phase 1, a total of 22 schools had more than half the places filled.
This is more than double the eight schools in last year's P1 registration exercise.
The results were announced by the Ministry of Education (MOE) on its website yesterday.
Phase 1 is for children whose siblings are currently studying in their primary school of choice.
Junyuan Primary School topped the list with 67 per cent of places taken. Out of its 180 spots, 120 were filled. Frontier Primary School saw 135 of 240 places taken (56 per cent), while Radin Mas Primary School had 115 of 210 spots filled (55 per cent).
Other schools with more than the usual share of siblings include Rosyth Primary School, with 156 of 300 spots taken, and Henry Park Primary School, with 160 of its 300 places filled.
Other popular schools still have more than half of P1 places available.
At Raffles Girls' Primary School, 64 of its 270 places have been filled. Rulang Primary School saw 114 of its 270 slots taken up, while Ai Tong School still has 206 of its 330 places available.
To cater to the larger number of Dragon Year babies born in 2012 who are starting P1 next year, there will be 2,600 more places available, Education Minister Ong Ye Kung had said on Wednesday. This brings the number to about 41,800 places in the 184 primary schools.
Six-year-old Celeste Lee will be joining her older siblings, nine-year-old Cherise and Kayson, seven, at Chong Fu Primary School in Yishun. Their mother Lee Ah Nee, 41, who works in the legal department of a life sciences firm, hopes this means an easier time for her youngest.
"When Cherise entered primary school, it took her about three months to get used to how different it was from her childcare centre. Celeste knows she has her jie jie (older sister) and kor kor (older brother) in the same school, so she is already more at ease."
Ms Jennifer Chong, 41, was thinking about trying for a place at Rosyth for her six-year-old son Joel. But that could mean having to go through a ballot in a later registration phase. So she decided to register him in Poi Ching School in Tampines, where his brother Jonas is studying.
"With both my sons in one school, my husband and I can take them to school together," said Ms Chong, who is in administration. "Besides, my heart is too weak to go through balloting."
Phase 2A(1) of the registration starts on Wednesday. It is for children whose parents are members of the alumni association of the school they want to apply to, or members of the school advisory or management committee.
Correction note: An earlier version of this story said that there were 17 primary schools with over half the places filled after Phase 1 of Primary 1 registration. It was actually after day one of Phase 1. We are sorry for the error.