There is enough supply to cope with the demand. The Government is carefully balancing supply with demand.
One of the upcoming EC launches is in Yio Chu Kang Road (next to Regentville private condo) and opposite Hougang 1 shopping Mall. It is within 1 km to the (popular) Rosyth Pri School. However, it could be challenging to enter via the competitive Phase 2C (for those living within 1 km). Same applies to those who live within 1 km of Nan Chiau Pri School.
There are also other upcoming EC and private condo in Sengkang (likely to launch next year).
What is important is prospective buyers buy their choice units carefully and not rush to commit any unit. Once OTP signed, termination fee applies.
Read widely, do more research, visit more showrooms, attend more property launches (if opportunity arises to have a better feel of buying during property launch), talk to different people (developers, agents, bankers, investors, those who have bought ECs, private condos, BTOs...), be open to ideas...
I'm sure you will eventually get your choice unit, whether is TC or other EC/ private condo/ BTO that best meet your family needs and one that can fit your finances.