Your dog is 10 months old and 55 pounds. A child comes through the door, or runs across the garden, and both front feet land on their chest or their shoulders.
With an adult, this is a muddy coat and an apology. With a 5 year old, it is a child on the floor. The behaviour is ordinary and the consequence is not.
Why children specifically
Children move fast, in short bursts, at low height, making high sounds. To an adolescent dog that reads as an invitation to play, and jumping is how a dog accepts it.
Children also pay for it without meaning to. Squealing, running away and flapping hands are all reward, and every jump that produces them has been paid.
A child cannot hold the standard you need. Asking a 6 year old to stand still and ignore a jumping dog is asking for something adults find hard.
Safety note
Get help now if there is stiffening, a hard stare, a growl, a raised lip, teeth used near a child's face, or any broken skin. Separate your dog from children completely, book a veterinary examination, and speak to a qualified behaviour professional. Sudden behaviour change warrants that examination, and pain frequently presents as a change in behaviour rather than as obvious lameness. Do not work on a bite risk around children on your own.
This week: manage the flashpoints
Behaviour change is built from management plus reinforcement together. Management is what stops the jumping being rehearsed while the greeting is still being built.
Name your 2 predictable flashpoints, usually the school pickup return and the hour before dinner. Put a gate or a door between your dog and the running at those times, every day.
Leave a light 6 foot house line on your dog's harness while children are up and moving. An adult picks up the line and leads the dog away, so no child ever has to.
Put something legal in your dog's mouth before the children arrive home. A dog already carrying a toy is not landing on anybody.
Teach the children one rule they can manage: stand still, fold your arms, and walk to a grown-up. Stillness ends the game faster than shouting does.
Adults handle the dog. Children are never given the job of correcting or controlling them.
Teach the greeting your dog can do instead
A dog cannot jump and keep 4 feet on the floor at the same time, so the floor is the behaviour to pay. Build it with adults first, because a real child arriving is too exciting to practise on.
Stand still with 15 treats. Every 2 seconds that all 4 feet stay down, feed 1 treat low, at your dog's chest height. Feeding low keeps the feet low.
Have an adult helper walk up and stop 6 feet away, then step 2 feet closer only while the feet are down. Any jump and the helper turns and walks quietly back.
Do 6 approaches and stop. Feet on the floor bring the person closer, jumping sends the person away.
Then recruit 1 older, calm child you know well, with the dog on the lead and an adult holding it. Three minutes, then put your dog away while it is still going well.
Ask the child to crouch rather than lean over, and to stroke the chest rather than the head.
Children you meet outside
Shorten the lead to 3 feet before a child gets close, and stand between them. Do not hand the lead to your own child in that moment.
Say no to greetings you cannot manage today. You do not owe a stranger an explanation, and plenty of children are frightened of dogs.
Practise at a distance your dog can manage. Feed 1 treat at your leg every time children pass at 30 feet, whether your dog looked at them or not.
If your dog will not take food, you are too close. Add 10 feet rather than repeating the cue.
When to separate entirely
Some weeks the honest answer is that your dog and the children are not in the same room. That is not a failure, and it is the safest thing you can do while the skill is thin.
Separate for chase games, trampolines, scooters, bikes and anything with squealing.
Separate for toddlers, who cannot stand still and go down easily.
Separate when everyone is tired at the end of the day, which is when supervision usually slips.
Never leave an adolescent dog and a child in a room together without an adult watching the dog.
Punishment is the wrong tool here for a practical reason as well as an evidence one. Punishment-based approaches are associated with fear, avoidance and defensive aggression, around exactly the people you are protecting. Reward-based methods are what the veterinary behaviour guidance recommends.
What to expect
Your dog will hold 4 feet down for an adult weeks before they manage it for a running child. That order is normal, and responsiveness to your cues does come back later in adolescence.
Today's version, in one line: the gate goes up at 4pm, and 15 treats get fed low for 4 feet on the floor.