Excluding a dog from family life every time children play teaches him that playtime means exile, and exiled dogs often return more frantic, not less. The better goal is a dog who understands the play area has an edge, who is genuinely content just outside it, and who still feels like a member of the household — close enough to watch, be talked to and be included, without wandering through towers, train tracks and small, precious constructions.
Choose a boundary he can actually see
Dogs do not understand invisible lines drawn by furniture arrangement and hope. Mark the edge of the play area with something physical and consistent: the border of a large rug, a low line of cushions, the edge of a play mat, or a row of storage boxes that also keeps toys contained. Keep the boundary in the same place every day, because a line that moves with tidying is a line he cannot learn. Place his own mat a short distance outside it — near enough that he is part of the room's life, far enough that a wagging tail and a stretching dog do not demolish the play — and make that mat comfortable, with his water bowl within his side of the line.
Teach the edge as a rewarding place to be
Train the boundary as a game before children are playing at full volume. Walk him towards the line on a lead, stop at the edge, reward him for turning back to his mat, and settle him there with a chew. Repeat in short sessions, gradually adding the sights and sounds of play — a tower being built, a toy car crossing the rug — while he practises staying on the mat and being paid handsomely for it. If he steps over the line, guide him out calmly without scolding and make the next repetition easier. What you are building is an association: the mat beside the play area is where treats, chews and calm attention happen, and the play area itself is simply uninteresting by comparison.
Keep him included from his side of the line
Inclusion is what stops boundary training from feeling like punishment. Talk to him while the children play. Let the children take turns coming out of the play area to give him an approved treat or ask for a trick he knows. Give him his own occupation alongside theirs — a long-lasting chew, a snuffle mat or a stuffed toy that arrives when play starts and is picked up when it ends, so playtime predicts good things for him too.
Coach the children as carefully as the dog
The boundary runs in both directions, and children need their half of the training. Toys, especially the small and squeaky kind, stay inside the play area; food never crosses the line in either direction; and nobody calls the dog into the play area as a joke or drags him in to join a game. Children should know his exit signs too — if he takes himself to his mat or further away, he is choosing rest and is left alone.
Proof the habit in ordinary, untidy moments
Boundary habits are tested not during training sessions but when a ball rolls out, a toddler heads for the dog with a biscuit, or three children arrive for a playdate. Manage those moments rather than hoping the training holds alone: an adult nearby during playdates, his chew refreshed when excitement rises, and the mat moved no further away than he can handle. Noting who runs his practice sessions and who supervises each play session in KinsLe using Care Teams keeps the boundary consistent, with every adult rewarding the same behaviour at the same line.