A new baby is wonderful news for the family and potentially catastrophic news for your toddler, who until now has enjoyed undivided attention. The good news: most children adjust well. But the adjustment takes months, not days.
Timing the conversation
Under two: a few weeks before the due date is enough - they have no concept of future time. Two to three: a couple of months gives them time to process. Use concrete language: "There's a baby growing in Mummy's tummy." Books about new siblings are genuinely helpful.
Expect regression
A potty-trained child may start having accidents. A child who slept through may start waking. A cheerful toddler may become clingy or have more tantrums. This isn't them being difficult - it's them processing a seismic shift with limited emotional tools.
Practical preparation
If you're planning changes - moving to a bed, starting nursery, dropping a dummy - do it well before or well after the baby arrives. Have your toddler "help" with baby preparations. Protect one-on-one time fiercely - even fifteen minutes of focused attention while someone else holds the baby makes a measurable difference.
When the baby arrives
Never leave a toddler unsupervised with a newborn - not because they're malicious, but because toddlers are impulsive and don't understand fragility. Most sibling jealousy peaks in the first three to six months and gradually settles.