HOUSTON -

A man is facing charges for allegedly hiding in the backseat of a mother's vehicle, then popping up and threatening her kids with a knife to get money to buy drugs.

Ismael Martinez is charged with aggravated robbery with a deadly weapon. It all started back on June 14 when the victim and her two children -- ages 5 and 2 -- went to a Kroger on N. Alexander Drive in Baytown. Before entering the grocery store the victim told investigators she noticed Martinez standing outside.

After shopping, the victim says she and her children got back into her vehicle and drove across the street to a CVS, where they shopped and returned to the vehicle. After exiting from the parking lot, she says Martinez then raised up from behind the third row seating and demanded money or her children would be harmed. She told police Martinez was holding a pocket knife.

Court documents state she yelled to her 5-year-old, who was seated in the third row, to come to the front, but Martinez grabbed the child and sat the child back down.

The woman told investigators Martinez gave her instructions where to drive and demanded $200. She told him she only had $20. She told police Martinez then came and sat in the front passenger seat and put the knife to her throat.

The victim says she was fighting with Martinez, trying to grab the knife, when he bit her on her hand. She told investigators she tried to crash into a telephone pole because Martinez was not wearing a seat belt, but Martinez grabbed the wheel and steered around the pole.

According to court documents, the vehicle then ran over a curb and into a field. The woman says she was able to stop the vehicle and told Martinez to get out. He exited and ran in front of the vehicle, at which point she says she accelerated and ran over Martinez.

Baytown police say Martinez told them was he strung out on meth and was looking to buy more drugs, but didn't have any money. When the woman was in Kroger, Martinez says he slipped into the woman's vehicle and hit in the very back. Police say he admitted to doing everything the woman said he did.

Court records show Martinez, 53, has prior convictions for arson in 1990 and sexual assault in 1976.