The question

I love my three-year-old son dearly, but I'm worried about his behaviour. He comes from a happy family and is an only child. His father and I are both in our late forties, and I am a full-time mum to him. Yet he can be extremely aggressive towards us and particularly towards other children. He bites, pushes and sometimes even snarls! I pull him up when he's been naughty, but I suppose I don't always follow through on my threats - could that be part of the problem? I spend my whole time apologising to other people's children and telling him off, and I've noticed other mums have stopped inviting us round to play. Yet other times my son is the most loving, gentle child. What can I do to help him?

The psychiatrist

Most of the time, such aggressive behaviour is simply an effective way for children to get what they want. Given he has a loving family, it's unlikely your son's behaviour is malicious. Sticking to clear limits, dealing firmly with unwanted behaviour and, most importantly, offering praise and attention for good behaviour all help a child's conduct. Grasp the nettle now: two-thirds of toddlers with behaviour problems at three still have them five years later. Use a special 'firm' tone of voice to tell your son off, and don't smile. Discuss your rules with adults who look after your son (his father, grandparents, teachers, etc) so that there is a consistent approach. He may just need more assistance from adults to structure his play and help him learn how to share, as children develop these skills at different ages. If you're still worried, call YoungMinds' free parenting-advice line (0800 018 2138)

·Professor David Cottrell is a trustee of the mental health charity YoungMinds and professor of child and adolescent psychiatry at the University of Leeds

The mother

My son Christian went through a very difficult stage when he was a toddler, and my husband and I were totally exhausted by it. Christian couldn't communicate verbally very well at the time, so he took his frustration out by pushing and biting us and other children. We really did try everything! He was too young to understand sticker charts or toys being removed, and naughty corners didn't work. However, I was consistent in removing him from the source of fun if he was naughty - at playgroup I'd take him outside the room to tell him off, but make sure he could still see the others enjoying themselves. On the biting front, a teacher suggested next time he was set to bite, I slip a bar of soap in his mouth. That sounds draconian, but it really worked. He hasn't bitten since. Now he's four and is a perfectly normal happy child, and the problems seem a long time ago. Be firm, and I'm sure your little boy will come out the other side, too.

·Julia Collins is a full-time mother of one from Buckinghamshire

The parenting journalist

Three-year-olds love attention, even if it's just the attention of being told off, so your son needs to learn that aggressive behaviour doesn't reward him. Don't spend time apologising to others - they'd rather see you dealing with it. Why not find one friendly mum, explain the situation and ask if she can help you solve it? Take your son round to play, let him know that if he's aggressive you'll take him straight home, and stick to your word. Then praise him when he plays well. Also, pre-empt his aggression. If you feel he's getting frustrated, let him channel his anger in other ways - kicking a ball outside or jumping or dancing to 'shake out' the frustration. There's plenty of easy-to-follow advice in New Toddler Taming by Dr Christopher Green (£12.99, Vermillion) and Steve Biddulph's The Secret of Happy Children (£8.99, HarperCollins). If you're still worried, talk to your health visitor or call 0808 800 2222, the 24-hour free, confidential helpline run by family charity Parentline Plus.

· Susie Boone is the editor of Practical Parenting magazine

· If you have a question for our experts, email health@observer.co.uk