Q.I know that 4-year-olds are rather self-absorbed, but I'm concerned about our grandson.

He is intelligent and likable, like his dad, but he won't take no for an answer, no matter how much his behavior bothers other people. Instead he cries or hits or just keeps doing what he's doing when he doesn't get exactly what he wants.

We try to pick our battles, but everything turns into a fight.

We see our grandson and his 9-month-old sister about four times a week, either when we baby-sit or when our daughter and the children come over for supper while her husband is at work. Each time we have the same problems.

When our grandson plays outside with his grandpa -- which he loves to do -- he acts up when it's time to come in. When we tell him to eat supper at the table -- instead of on a tray in front of the TV -- he negotiates to sit at the edge of the kitchen, and when it's time to go home, he pulls out another toy and refuses to put it away.

I know our grandson also acts up at school and that our daughter tends to give in to him, but she says she handles both kids successfully at night when she is alone with them or when she tells her son no and that he only misbehaves when my husband and I are around.

Does our grandson act up because he is jealous of his baby sister, even though he seems to love her? Is he reacting to something in his diet? Or is he a plain old garden-variety brat?

A.Sibling rivalry or the wrong diet often affects a child's behavior, but in this case your grandson is probably reacting to the limits he gets -- and doesn't get.

Every child needs clear boundaries at every age to feel safe and protected. Unless parents -- and grandparents -- set these limits, and stick by them, he will push and push until he knows where he stands.

Parents and grandparents needn't have the same limits, however, for children will accept different boundaries as long as the rules are clear and they know that their parents always have the last word. As much as you'd like an equal say, you only can tell your grandson what he can and can't do if he is about to make a big mess at your house or break something or pull the cat's tail.

Rules aren't chiseled in stone, either. A child can be allowed to dawdle occasionally, or to eat supper in front of the TV when he's feeling punky, but only after he's quit trying to negotiate everything you ask him to do. Until then, you have to be quite firm.

Although every family rears their children in their own style, only one kind of discipline is truly effective.

If rules are too strict, a child will usually be exceptionally well-behaved until he's a teenager, and then suddenly he will rear up and say, "Yeah, you and who else are going to make me?" Having shot every arrow in their quiver, the parents become permissive and let him do whatever he wants. If their discipline is too lax, however, the child becomes increasingly obnoxious and by adolescence his parents get very tough with him because they just can't stand his behavior any more.

In discipline, as in most things, the middle road works best.

You and his mom will follow it more easily if you quit taking the whims of your grandson so seriously. Listen to him, be understanding and sympathetic when he wants to do something you don't want him to do, and then give him a hug, an authoritative "no" and change the subject.

You also have to prepare him for each transition. When he wants to play outside, his grandpa should tell him that he will get a five-minute warning and then he'll have to go inside when the time is up. When he doesn't, your husband should pick up the boy and carry him into the house, without a smile or a lecture, just as his mom should carry him to the car when it's time to leave. The more grown-ups ignore a child's caterwauling, the less he will cry and hit.

And when he wants to eat in front of the TV, tell him that he must first learn to eat at the table. These techniques may sound stern, but they will teach your grandson that some things are not negotiable.

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