We took our kids on a day trip to Tikal in November 2002. We took a van from San Ignacio, and didn't run into any trouble on the road. However, as Mayaphile said, the political situation is very fluid, so be sure to check before you go.
My husband and I took turns climbing Temple 2 (we deemed it too dangerous for the kids). The steps are VERY steep, VERY narrow, with NO handrails, and NO guard rails. The ledge at the top of the steps seems to be a few stories from the ground. When I got back down, I asked our guide if anyone had ever fallen. He shrugged his shoulders and said, "Eh..not many." That struck me as pretty funny.
We did let the kids climb Temple 4. It was an awesome sight, and the sound of howler monkeys floating above the canopy is something I will always remember.
Tikal is a fabulous place, and I hope you and your kids are able to go.