need some advise for kids computer

Those are some pretty old systems. You're best ditching them and going one of two routes:

a) Limit their access under limited accounts on your computer and password protect your account. If you got Vista you can setup some parental controls as well depending on their age, block downloads that could potentially harm your PC by them, and limit the times they're allowed to use the computer.
b) Make it a holiday gift and invest in some newer systems. For as little as 200-300$ now days you can get an even better system then the systems you've mentioned above.