For past few days, my 3 year old has been consistently waking up 4 hours after bedtime on the dot! He always goes to bed at 10 & waking up crying at 2 a.m! Me & my wife cant seem to figure out why..he will cry on & off until 6 a.m where he finally fell asleep again. This has been distrupting his school time (insufficient sleep and both me & my wife haven't got enough sleep ever since.
Anyone encounter such problem before?

Yes. currently my wife is pregnant with our soon to be 2nd child..